Opt-in TCO (#1219)

build.sbt

@@ -415,6 +415,8 @@ lazy val syntax = crossProject(JVMPlatform, JSPlatform)
   .configs(Test)
   .configs(Benchmark)
   .settings(
+    commands += WithDebugCommand.withDebug,
+    Test / fork := true,
     testFrameworks := Nil,
     scalacOptions ++= Seq("-Ypatmat-exhaust-depth", "off"),
     mainClass in (Compile, run) := Some("org.enso.syntax.text.Main"),

distribution/std-lib/Base/src/Bench_Utils.enso

@@ -2,27 +2,31 @@ from Base import all
 
 reverse_list = list ->
     go = list -> acc -> case list of
-        Cons h t -> go t (Cons h acc)
+        Cons h t -> @Tail_Call go t (Cons h acc)
         Nil -> acc
-    go list Nil
+    res = go list Nil
+    res
 
 sum_list = list ->
     go = list -> acc -> case list of
-        Cons a b -> go b (acc + a)
+        Cons a b -> @Tail_Call go b (acc + a)
         Nil -> acc
 
-    go list 0
+    res = go list 0
+    res
 
 avg_list = list -> here.sum_list list / here.len_list list
 
 len_list = list ->
     go = list -> acc -> case list of
-        Cons _ b -> go b (acc + 1)
+        Cons _ b -> @Tail_Call go b (acc + 1)
         Nil -> acc
-    go list 0
+    res = go list 0
+    res
 
 Number.times = act ->
-    go = results -> number -> if number == 0 then results else go (Cons (act number) results) number-1
+    go = results -> number -> if number == 0 then results else
+        @Tail_Call go (Cons (act number) results) number-1
     res = here.reverse_list (go Nil this)
     res
 

distribution/std-lib/Base/src/List.enso

@@ -12,7 +12,7 @@ map_helper list cons f = case list of
     Cons h t ->
         res = Cons (f h) Nil
         Unsafe.set_atom_field cons 1 res
-        here.map_helper t res f
+        @Tail_Call here.map_helper t res f
     Nil -> Unsafe.set_atom_field cons 1 Nil
 
 ## The basic cons-list type.
@@ -53,11 +53,14 @@ type List
          to the standard output:
              (Cons 0 <| Cons 1 <| Cons 2 <| Nil) . each IO.println
     each : (Any -> Any) -> Unit
-    each f = case this of
-        Nil -> Unit
-        Cons h t ->
-            f h
-            t.each f
+    each f =
+        go list = case list of
+            Nil -> Unit
+            Cons h t ->
+                f h
+                @Tail_Call go t
+        res = go this
+        res
 
     ## Combines all the elements of the list, by iteratively applying the
        passed function with next elements of the list.
@@ -75,7 +78,7 @@ type List
     fold init f =
         go acc list = case list of
             Nil -> acc
-            Cons h t -> go (f acc h) t
+            Cons h t -> @Tail_Call go (f acc h) t
         res = go init this
         res
 
@@ -98,7 +101,10 @@ type List
          larger than `1`:
              (Cons 0 <| Cons 1 <| Cons 2 <| Nil) . any (> 5)
     any : (Any -> Boolean) -> Boolean
-    any predicate = case this of
-        Nil -> False
-        Cons h t -> if predicate h then True else t.any predicate
-
+    any predicate =
+        go list = case list of
+            Nil -> False
+            Cons h t -> if predicate h then True else
+                @Tail_Call go t
+        res = go this
+        res

distribution/std-lib/Base/src/Main.enso

@@ -33,7 +33,7 @@ type Range
     each function =
         it start end = if start == end then Unit else
             function start
-            it start+1 end
+            @Tail_Call it start+1 end
         it this.start this.end
         Unit
 
@@ -52,7 +52,7 @@ type Range
     fold initial function =
         it acc start end = if start == end then acc else
             new_acc = function acc start
-            it new_acc start+1 end
+            @Tail_Call it new_acc start+1 end
         res = it initial this.start this.end
         res
 
@@ -60,7 +60,7 @@ type Range
     every predicate =
         it start end = if start==end then True else
             r = predicate start
-            if r then (it start+1 end) else False
+            if r then (@Tail_Call it start+1 end) else False
         res = it this.start this.end
         res
 

distribution/std-lib/Base/src/System/File.enso

@@ -167,8 +167,7 @@ type File
     read_bytes : Vector ! File_Error
     read_bytes =
         opts = [Option.Read]
-        bytes = this.with_input_stream opts (_.read_all_bytes)
-        bytes
+        this.with_input_stream opts (_.read_all_bytes)
 
     ## Reads the whole file into a `Text`, assuming UTF-8 content encoding.
     read : Text ! File_Error

distribution/std-lib/Base/src/Text/Extensions.enso

@@ -24,7 +24,7 @@ Text.each function =
     iterate prev nxt = if nxt == -1 then Unit else
         function (Text_Utils.substring [this, prev, nxt])
         next_nxt = iterator.next []
-        iterate nxt next_nxt
+        @Tail_Call iterate nxt next_nxt
     iterate fst nxt
     Unit
 
@@ -39,8 +39,7 @@ Text.characters : Vector
 Text.characters =
     bldr = Vector.new_builder
     this.each bldr.append
-    r = bldr.to_vector
-    r
+    bldr.to_vector
 
 ## Takes a separator string and returns a vector resulting from splitting
    `this` on each occurence of `separator`.

distribution/std-lib/Base/src/Vector.enso

@@ -53,11 +53,7 @@ type Vector
     ## Converts a polyglot value representing an array into a vector. This is
        useful when wrapping polyglot APIs for further use in Enso.
     from_polyglot_array : Any -> Vector
-    from_polyglot_array arr =
-        a = Array.new arr.length
-        0.upto arr.length . each i->
-            a.set_at i (arr.at i)
-        Vector a
+    from_polyglot_array arr = Vector.new arr.length arr.at
 
     ## Returns the number of elements stored in this vector.
     length : Number
@@ -79,8 +75,7 @@ type Vector
     fold initial function =
         arr = this.to_array
         f = acc -> ix -> function acc (arr.at ix)
-        res = 0.upto this.length . fold initial f
-        res
+        0.upto this.length . fold initial f
 
     ## Creates a new vector of the given length, initializing elements using
        the provided constructor function.
@@ -146,8 +141,7 @@ type Vector
         arr1 = this.to_array
         arr2 = that.to_array
         eq_at i = arr1.at i == arr2.at i
-        r = if arr1.length == arr2.length then 0.upto arr1.length . every eq_at else False
-        r
+        if arr1.length == arr2.length then 0.upto arr1.length . every eq_at else False
 
     ## Concatenates two vectors, resulting in a new vector, containing all the
        elements of `this`, followed by all the elements of `that`.

docs/runtime/builtin-base-methods.md

@@ -42,11 +42,6 @@ should be treated as a builtin method. It takes the following arguments:
 2. `name` **String** the method name.
 3. `description` **String** a summary of the method's behavior, for
    documentation purposes.
-4. `alwaysDirect` **Boolean = `true`** describes whether the function can always
-   be safely called directly. It should be set to `false` for methods that
-   evaluate user code in a tail position (e.g. `if_then_else`). If the method
-   does not take functions or thunks as parameters, or it only evaluates these
-   in a non-tail position, this parameter should be left defaulted.
 
 The annotation will generate a `RootNode` subclass in the same package as the
 declaring node, with a name basing on the declaring node's name. The name of the

docs/runtime/function-call-flow.md

@@ -46,7 +46,7 @@ like a builtin language loop construct.
 In pseudocode, a tail recursive function, like:
 
 ```ruby
-foo x = if x == 0 then print "foo" else foo (x - 1)
+foo x = if x == 0 then print "foo" else @Tail_Call foo (x - 1)
 ```
 
 becomes:

docs/semantics/tail-call-optimization.md

@@ -0,0 +1,79 @@
+---
+layout: developer-doc
+title: Managed Resources
+category: semantics
+tags: [resources, finalization, cleanup]
+order: 10
+---
+
+# Tail Call Optimization
+
+Tail call optimization is a powerful technique for optimizing functional
+programs. It allows transforming recursive functions of certain shapes into
+loops, removing unnecessary intermediate function calls and saving stack space.
+This document outlines the usage and semantics of tail call optimization in
+Enso.
+
+<!-- MarkdownTOC levels="2,3" autolink="true" -->
+
+- [Tail Calls](#tail-calls)
+- [Usage](#usage)
+
+<!-- /MarkdownTOC -->
+
+## Tail Calls
+
+A Tail Call is a function call occurring as the last statement in a function
+body, i.e. an expression whose value is guaranteed not to be depended upon by
+the function itself. For example,
+
+```hs
+sum_1 n = if n == 0 then 0 else 1 + sum_1 n-1
+
+sum_2 n acc = if n == 0 then acc else @Tail_Call sum_2 n-1 acc+n
+```
+
+In the code snippet above, only the `sum_2` function is tail recursive. The
+result of calling `sum_2` recursively is not depended upon by `sum_2` itself or
+the definition of `if_then_else` method on booleans. On the other hand, `sum_1`
+needs to know the value of its recursive call in order to perform the addition
+operation. It is advised that functions that can be expressed with tail-calls
+are implemented that way. Using tail call optimization, will lead to `sum_2`
+being orders of magnitude faster than `sum_1`. Moreover, for `n = 100000000`,
+`sum_1` will allocate a hundred million stack frames (over a gigabyte, likely
+resulting in a stack overflow error), while `sum_2` is an allocation-free loop.
+
+## Usage
+
+Enso does not currently perform automatic tail call detection and defers the
+optimization decisions to the user. To mark a function call as a tail call, the
+`@Tail_Call` annotation must be used. Note that if the annotation is placed
+incorrectly, it may either be reported as a warning by the compiler, or silently
+ignored if such analysis is impossible to perform due to the compiler's limited
+static analysis capabilities. However, it is _guaranteed_ that a wrongly placed
+`@Tail_Call` annotation will not lead to incorrect runtime behavior.
+
+If the `@Tail_Call` annotation is not placed, the call will be treated as a
+standard on-stack function call.
+
+For example, the following code reverses a list in a tail recursive fashion:
+
+```
+reverse list =
+    go list result = case list of
+        Nil -> result
+        Cons head tail -> @Tail_Call go tail (Cons head result)
+    result = go list Nil
+    result
+```
+
+Note the placement of `@Tail_Call` in the recursive branch of `go`. It is placed
+correctly, marking the last operation in a function, and therefore `go` will be
+interpreted as a loop rather than a chain of function calls.
+
+> #### Debugging Tail Calls
+>
+> The way `go` is wrapped in the example above is recommended for most uses.
+> Using the assignment and return of a variable, rather than a direct call,
+> guarantees that calls to `reverse` won't themselves be removed from the call
+> stack and therefore greatly aids debugging.

engine/runtime/src/bench/scala/org/enso/interpreter/bench/fixtures/semantic/AtomFixtures.scala

@@ -23,7 +23,7 @@ class AtomFixtures extends DefaultInterpreterRunner {
     """from Builtins import all
       |
       |main = length ->
-      |    generator = acc -> i -> if i == 0 then acc else generator (Cons i acc) (i - 1)
+      |    generator = acc -> i -> if i == 0 then acc else @Tail_Call generator (Cons i acc) (i - 1)
       |
       |    res = generator Nil length
       |    res
@@ -34,7 +34,7 @@ class AtomFixtures extends DefaultInterpreterRunner {
     """from Builtins import all
       |
       |main = length ->
-      |    generator = acc -> i -> if i == 0 then acc else generator (Builtins.cons i acc) (i - 1)
+      |    generator = acc -> i -> if i == 0 then acc else @Tail_Call generator (Builtins.cons i acc) (i - 1)
       |
       |    res = generator Builtins.nil length
       |    res
@@ -46,7 +46,7 @@ class AtomFixtures extends DefaultInterpreterRunner {
       |
       |main = list ->
       |    reverser = acc -> list -> case list of
-      |        Cons h t -> reverser (Cons h acc) t
+      |        Cons h t -> @Tail_Call reverser (Cons h acc) t
       |        Nil -> acc
       |
       |    res = reverser Nil list
@@ -58,7 +58,7 @@ class AtomFixtures extends DefaultInterpreterRunner {
     """from Builtins import all
       |
       |Cons.reverse = acc -> case this of
-      |    Cons h t -> reverse t (Cons h acc)
+      |    Cons h t -> @Tail_Call reverse t (Cons h acc)
       |
       |Nil.reverse = acc -> acc
       |
@@ -73,7 +73,7 @@ class AtomFixtures extends DefaultInterpreterRunner {
       |
       |main = list ->
       |    summator = acc -> list -> case list of
-      |        Cons h t -> summator acc+h t
+      |        Cons h t -> @Tail_Call summator acc+h t
       |        Nil -> acc
       |
       |    res = summator 0 list
@@ -86,7 +86,7 @@ class AtomFixtures extends DefaultInterpreterRunner {
       |
       |main = list ->
       |    fold = f -> acc -> list -> case list of
-      |        Cons h t -> fold f (f acc h) t
+      |        Cons h t -> @Tail_Call fold f (f acc h) t
       |        _ -> acc
       |
       |    res = fold (x -> y -> x + y) 0 list
@@ -99,7 +99,7 @@ class AtomFixtures extends DefaultInterpreterRunner {
       |
       |main = list ->
       |    summator = acc -> list -> case list of
-      |        Cons h t -> summator acc+h t
+      |        Cons h t -> @Tail_Call summator acc+h t
       |        _ -> acc
       |
       |    res = summator 0 list
@@ -112,7 +112,7 @@ class AtomFixtures extends DefaultInterpreterRunner {
       |
       |Nil.sum = acc -> acc
       |Cons.sum = acc -> case this of
-      |    Cons h t -> sum t h+acc
+      |    Cons h t -> @Tail_Call sum t h+acc
       |
       |main = list ->
       |    res = sum list 0
@@ -125,7 +125,7 @@ class AtomFixtures extends DefaultInterpreterRunner {
       |
       |Nil.mapReverse = f -> acc -> acc
       |Cons.mapReverse = f -> acc -> case this of
-      |    Cons h t -> mapReverse t f (Cons (f h) acc)
+      |    Cons h t -> @Tail_Call mapReverse t f (Cons (f h) acc)
       |
       |main = list ->
       |    res = mapReverse list (x -> x + 1) Nil
@@ -138,7 +138,7 @@ class AtomFixtures extends DefaultInterpreterRunner {
       |
       |Nil.mapReverse = f -> acc -> acc
       |Cons.mapReverse = f -> acc -> case this of
-      |    Cons h t -> mapReverse t f (Cons (f h) acc)
+      |    Cons h t -> @Tail_Call mapReverse t f (Cons (f h) acc)
       |
       |main = list ->
       |    adder = x -> y -> x + y

engine/runtime/src/bench/scala/org/enso/interpreter/bench/fixtures/semantic/NamedDefaultedArgumentFixtures.scala

@@ -9,7 +9,7 @@ class NamedDefaultedArgumentFixtures extends DefaultInterpreterRunner {
     """
       |main = sumTo ->
       |    summator = acc -> current ->
-      |        if current == 0 then acc else summator (current = current - 1) (acc = acc + current)
+      |        if current == 0 then acc else @Tail_Call summator (current = current - 1) (acc = acc + current)
       |
       |    res = summator current=sumTo acc=0
       |    res
@@ -20,7 +20,7 @@ class NamedDefaultedArgumentFixtures extends DefaultInterpreterRunner {
     """
       |main = sumTo ->
       |    summator = (acc = 0) -> current ->
-      |        if current == 0 then acc else summator (current = current - 1) (acc = acc + current)
+      |        if current == 0 then acc else @Tail_Call summator (current = current - 1) (acc = acc + current)
       |
       |    res = summator (current = sumTo)
       |    res

engine/runtime/src/bench/scala/org/enso/interpreter/bench/fixtures/semantic/RecursionFixtures.scala

@@ -12,7 +12,7 @@ class RecursionFixtures extends DefaultInterpreterRunner {
     """
       |main = sumTo ->
       |    summator = acc -> current ->
-      |        if current == 0 then acc else summator acc+current current-1
+      |        if current == 0 then acc else @Tail_Call summator acc+current current-1
       |
       |    res = summator 0 sumTo
       |    res
@@ -23,7 +23,7 @@ class RecursionFixtures extends DefaultInterpreterRunner {
     """
       |main = sumTo ->
       |    summator = acc -> i -> f ->
-      |        if i == 0 then acc else summator (f acc i) (i - 1) f
+      |        if i == 0 then acc else @Tail_Call summator (f acc i) (i - 1) f
       |    res = summator 0 sumTo (x -> y -> x + y)
       |    res
       |""".stripMargin
@@ -42,7 +42,7 @@ class RecursionFixtures extends DefaultInterpreterRunner {
     """
       |main = sumTo ->
       |    summator = acc -> i -> f ->
-      |        if i == 0 then acc else summator (f acc i) (i - 1) f
+      |        if i == 0 then acc else @Tail_Call summator (f acc i) (i - 1) f
       |    res = summator 0 sumTo (x -> y -> x + y)
       |    res
       |""".stripMargin
@@ -54,7 +54,7 @@ class RecursionFixtures extends DefaultInterpreterRunner {
       |stateSum = n ->
       |    acc = State.get Number
       |    State.put Number (acc + n)
-      |    if n == 0 then State.get Number else here.stateSum (n - 1)
+      |    if n == 0 then State.get Number else @Tail_Call here.stateSum (n - 1)
       |
       |main = sumTo ->
       |    res = State.run Number 0 (here.stateSum sumTo)
@@ -67,7 +67,7 @@ class RecursionFixtures extends DefaultInterpreterRunner {
       |
       |main = sumTo ->
       |    summator = acc -> current ->
-      |        if current == 0 then acc else Debug.eval "summator (acc + current) (current - 1)"
+      |        if current == 0 then acc else Debug.eval "@Tail_Call summator (acc + current) (current - 1)"
       |
       |    res = summator 0 sumTo
       |    res
@@ -79,7 +79,7 @@ class RecursionFixtures extends DefaultInterpreterRunner {
       |
       |doNTimes = n -> ~block ->
       |    block
-      |    if n == 1 then Unit else here.doNTimes n-1 block
+      |    if n == 1 then Unit else @Tail_Call here.doNTimes n-1 block
       |
       |main = n ->
       |    block =

engine/runtime/src/main/java/org/enso/interpreter/node/BaseNode.java

@@ -11,7 +11,17 @@ import com.oracle.truffle.api.nodes.NodeInfo;
 @NodeInfo(shortName = "Base", description = "A base node for the Enso AST")
 @ReportPolymorphism
 public abstract class BaseNode extends Node {
-  private @CompilationFinal boolean isTail = false;
+  /** Represents the tail-position status of the node. */
+  public enum TailStatus {
+    /** Node is in a tail position, but not marked as a tail call. */
+    TAIL_DIRECT,
+    /** Node is in a tail position and marked as a tail call. */
+    TAIL_LOOP,
+    /** Node is not in a tail position. */
+    NOT_TAIL
+  }
+
+  private @CompilationFinal TailStatus tailStatus = TailStatus.NOT_TAIL;
   private @CompilerDirectives.CompilationFinal FrameSlot stateFrameSlot;
 
   /**
@@ -28,30 +38,16 @@ public abstract class BaseNode extends Node {
   }
 
   /**
-   * Sets whether the node is tail-recursive.
+   * Sets the new tail position status for this node.
    *
-   * @param isTail whether or not the node is tail-recursive.
+   * @param tailStatus the new tail status.
    */
-  public void setTail(boolean isTail) {
-    this.isTail = isTail;
+  public void setTailStatus(TailStatus tailStatus) {
+    this.tailStatus = tailStatus;
   }
 
-  /** Marks the node as tail-recursive. */
-  public final void markTail() {
-    setTail(true);
-  }
-
-  /** Marks the node as not tail-recursive. */
-  public final void markNotTail() {
-    setTail(false);
-  }
-
-  /**
-   * Checks if the node is tail-recursive.
-   *
-   * @return {@code true} if the node is tail-recursive, otherwise {@code false}
-   */
-  public boolean isTail() {
-    return isTail;
+  /** @return the tail position status of this node. */
+  public TailStatus getTailStatus() {
+    return tailStatus;
   }
 }

engine/runtime/src/main/java/org/enso/interpreter/node/callable/ApplicationNode.java

@@ -65,9 +65,9 @@ public class ApplicationNode extends ExpressionNode {
    * @param isTail whether or not the node is tail-recursive.
    */
   @Override
-  public void setTail(boolean isTail) {
-    super.setTail(isTail);
-    invokeCallableNode.setTail(isTail);
+  public void setTailStatus(TailStatus isTail) {
+    super.setTailStatus(isTail);
+    invokeCallableNode.setTailStatus(isTail);
   }
 
   /**

engine/runtime/src/main/java/org/enso/interpreter/node/callable/IndirectInvokeCallableNode.java

@@ -9,6 +9,7 @@ import com.oracle.truffle.api.frame.Frame;
 import com.oracle.truffle.api.frame.MaterializedFrame;
 import com.oracle.truffle.api.frame.VirtualFrame;
 import com.oracle.truffle.api.nodes.Node;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.callable.InvokeCallableNode;
 import org.enso.interpreter.node.callable.dispatch.IndirectInvokeFunctionNode;
 import org.enso.interpreter.node.callable.thunk.ThunkExecutorNode;
@@ -51,7 +52,7 @@ public abstract class IndirectInvokeCallableNode extends Node {
       CallArgumentInfo[] schema,
       InvokeCallableNode.DefaultsExecutionMode defaultsExecutionMode,
       InvokeCallableNode.ArgumentsExecutionMode argumentsExecutionMode,
-      boolean isTail);
+      BaseNode.TailStatus isTail);
 
   @Specialization
   Stateful invokeFunction(
@@ -62,7 +63,7 @@ public abstract class IndirectInvokeCallableNode extends Node {
       CallArgumentInfo[] schema,
       InvokeCallableNode.DefaultsExecutionMode defaultsExecutionMode,
       InvokeCallableNode.ArgumentsExecutionMode argumentsExecutionMode,
-      boolean isTail,
+      BaseNode.TailStatus isTail,
       @Cached IndirectInvokeFunctionNode invokeFunctionNode) {
     return invokeFunctionNode.execute(
         function,
@@ -84,7 +85,7 @@ public abstract class IndirectInvokeCallableNode extends Node {
       CallArgumentInfo[] schema,
       InvokeCallableNode.DefaultsExecutionMode defaultsExecutionMode,
       InvokeCallableNode.ArgumentsExecutionMode argumentsExecutionMode,
-      boolean isTail,
+      BaseNode.TailStatus isTail,
       @Cached IndirectInvokeFunctionNode invokeFunctionNode) {
     return invokeFunction(
         constructor.getConstructorFunction(),
@@ -107,7 +108,7 @@ public abstract class IndirectInvokeCallableNode extends Node {
       CallArgumentInfo[] schema,
       InvokeCallableNode.DefaultsExecutionMode defaultsExecutionMode,
       InvokeCallableNode.ArgumentsExecutionMode argumentsExecutionMode,
-      boolean isTail,
+      BaseNode.TailStatus isTail,
       @Cached IndirectInvokeFunctionNode invokeFunctionNode,
       @Cached ThunkExecutorNode thisExecutor,
       @Cached MethodResolverNode methodResolverNode) {
@@ -117,7 +118,8 @@ public abstract class IndirectInvokeCallableNode extends Node {
     if (canApplyThis) {
       Object selfArgument = arguments[thisArgumentPosition];
       if (argumentsExecutionMode.shouldExecute()) {
-        Stateful selfResult = thisExecutor.executeThunk((Thunk) selfArgument, state, false);
+        Stateful selfResult =
+            thisExecutor.executeThunk((Thunk) selfArgument, state, BaseNode.TailStatus.NOT_TAIL);
         selfArgument = selfResult.getValue();
         state = selfResult.getState();
         arguments[thisArgumentPosition] = selfArgument;
@@ -146,7 +148,7 @@ public abstract class IndirectInvokeCallableNode extends Node {
       CallArgumentInfo[] schema,
       InvokeCallableNode.DefaultsExecutionMode defaultsExecutionMode,
       InvokeCallableNode.ArgumentsExecutionMode argumentsExecutionMode,
-      boolean isTail) {
+      BaseNode.TailStatus isTail) {
     throw new NotInvokableException(callable, this);
   }
 }

engine/runtime/src/main/java/org/enso/interpreter/node/callable/InteropApplicationNode.java

@@ -7,6 +7,7 @@ import com.oracle.truffle.api.nodes.Node;
 import com.oracle.truffle.api.nodes.NodeInfo;
 import org.enso.interpreter.Constants;
 import org.enso.interpreter.Language;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.callable.dispatch.IndirectInvokeFunctionNode;
 import org.enso.interpreter.node.callable.dispatch.InvokeFunctionNode;
 import org.enso.interpreter.node.expression.builtin.interop.syntax.HostValueToEnsoNode;
@@ -96,7 +97,7 @@ public abstract class InteropApplicationNode extends Node {
             buildSchema(arguments.length),
             InvokeCallableNode.DefaultsExecutionMode.EXECUTE,
             InvokeCallableNode.ArgumentsExecutionMode.PRE_EXECUTED,
-            false)
+            BaseNode.TailStatus.NOT_TAIL)
         .getValue();
   }
 }

engine/runtime/src/main/java/org/enso/interpreter/node/callable/InvokeCallableNode.java

@@ -185,7 +185,8 @@ public abstract class InvokeCallableNode extends BaseNode {
             lock.unlock();
           }
         }
-        Stateful selfResult = thisExecutor.executeThunk((Thunk) selfArgument, state, false);
+        Stateful selfResult =
+            thisExecutor.executeThunk((Thunk) selfArgument, state, TailStatus.NOT_TAIL);
         selfArgument = selfResult.getValue();
         state = selfResult.getState();
         arguments[thisArgumentPosition] = selfArgument;
@@ -233,9 +234,9 @@ public abstract class InvokeCallableNode extends BaseNode {
    * @param isTail whether or not the node is tail-recursive.
    */
   @Override
-  public void setTail(boolean isTail) {
-    super.setTail(isTail);
-    invokeFunctionNode.setTail(isTail);
+  public void setTailStatus(TailStatus isTail) {
+    super.setTailStatus(isTail);
+    invokeFunctionNode.setTailStatus(isTail);
   }
 
   /** @return the source section for this node. */

engine/runtime/src/main/java/org/enso/interpreter/node/callable/argument/ArgumentSorterNode.java

@@ -82,7 +82,8 @@ public class ArgumentSorterNode extends BaseNode {
     }
     for (int i = 0; i < mapping.getArgumentShouldExecute().length; i++) {
       if (executors[i] != null) {
-        Stateful result = executors[i].executeThunk(TypesGen.asThunk(arguments[i]), state, false);
+        Stateful result =
+            executors[i].executeThunk(TypesGen.asThunk(arguments[i]), state, TailStatus.NOT_TAIL);
         arguments[i] = result.getValue();
         state = result.getState();
       }

engine/runtime/src/main/java/org/enso/interpreter/node/callable/argument/IndirectArgumentSorterNode.java

@@ -6,6 +6,7 @@ import com.oracle.truffle.api.dsl.Specialization;
 import com.oracle.truffle.api.nodes.ExplodeLoop;
 import com.oracle.truffle.api.nodes.Node;
 import com.oracle.truffle.api.nodes.NodeInfo;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.callable.InvokeCallableNode;
 import org.enso.interpreter.node.callable.thunk.ThunkExecutorNode;
 import org.enso.interpreter.runtime.callable.argument.CallArgumentInfo.ArgumentMapping;
@@ -42,7 +43,8 @@ public abstract class IndirectArgumentSorterNode extends Node {
     for (int i = 0; i < mapping.getArgumentShouldExecute().length; i++) {
       if (TypesGen.isThunk(arguments[i]) && mapping.getArgumentShouldExecute()[i]) {
         Stateful result =
-            thunkExecutorNode.executeThunk(TypesGen.asThunk(arguments[i]), state, false);
+            thunkExecutorNode.executeThunk(
+                TypesGen.asThunk(arguments[i]), state, BaseNode.TailStatus.NOT_TAIL);
         arguments[i] = result.getValue();
         state = result.getState();
       }

engine/runtime/src/main/java/org/enso/interpreter/node/callable/dispatch/CurryNode.java

@@ -21,7 +21,6 @@ import java.util.concurrent.locks.Lock;
 /** Handles runtime function currying and oversaturated (eta-expanded) calls. */
 @NodeInfo(description = "Handles runtime currying and eta-expansion")
 public class CurryNode extends BaseNode {
-  private final FunctionSchema preApplicationSchema;
   private final FunctionSchema postApplicationSchema;
   private final boolean appliesFully;
   private @Child InvokeCallableNode oversaturatedCallableNode;
@@ -31,14 +30,12 @@ public class CurryNode extends BaseNode {
   private final InvokeCallableNode.DefaultsExecutionMode defaultsExecutionMode;
 
   private CurryNode(
-      FunctionSchema originalSchema,
       FunctionSchema postApplicationSchema,
       InvokeCallableNode.DefaultsExecutionMode defaultsExecutionMode,
       InvokeCallableNode.ArgumentsExecutionMode argumentsExecutionMode,
-      boolean isTail) {
-    setTail(isTail);
+      BaseNode.TailStatus isTail) {
+    setTailStatus(isTail);
     this.defaultsExecutionMode = defaultsExecutionMode;
-    this.preApplicationSchema = originalSchema;
     this.postApplicationSchema = postApplicationSchema;
     appliesFully = postApplicationSchema.isFullyApplied(defaultsExecutionMode);
     initializeCallNodes();
@@ -48,32 +45,27 @@ public class CurryNode extends BaseNode {
   /**
    * Creates a new instance of this node.
    *
-   * @param preApplicationSchema the schema of all functions being used in the {@link
-   *     #execute(VirtualFrame, Function, CallerInfo, Object, Object[], Object[])} method.
    * @param argumentMapping the argument mapping for moving from the original schema to the argument
    *     schema expected by the function.
    * @param defaultsExecutionMode the mode of handling defaulted arguments for this call.
    * @param argumentsExecutionMode the mode of executing lazy arguments for this call.
-   * @param isTail is this a tail call position?
+   * @param tailStatus is this a tail call position?
    * @return an instance of this node.
    */
   public static CurryNode build(
-      FunctionSchema preApplicationSchema,
       CallArgumentInfo.ArgumentMapping argumentMapping,
       InvokeCallableNode.DefaultsExecutionMode defaultsExecutionMode,
       InvokeCallableNode.ArgumentsExecutionMode argumentsExecutionMode,
-      boolean isTail) {
+      BaseNode.TailStatus tailStatus) {
     return new CurryNode(
-        preApplicationSchema,
         argumentMapping.getPostApplicationSchema(),
         defaultsExecutionMode,
         argumentsExecutionMode,
-        isTail);
+        tailStatus);
   }
 
   private void initializeCallNodes() {
-    if (postApplicationSchema.hasOversaturatedArgs()
-        || !preApplicationSchema.getCallStrategy().shouldCallDirect(isTail())) {
+    if (postApplicationSchema.hasOversaturatedArgs() || getTailStatus() == TailStatus.NOT_TAIL) {
       this.loopingCall = CallOptimiserNode.build();
     } else {
       this.directCall = ExecuteCallNode.build();
@@ -88,7 +80,7 @@ public class CurryNode extends BaseNode {
               postApplicationSchema.getOversaturatedArguments(),
               defaultsExecutionMode,
               argumentsExecutionMode);
-      oversaturatedCallableNode.setTail(isTail());
+      oversaturatedCallableNode.setTailStatus(getTailStatus());
     }
   }
 
@@ -159,12 +151,13 @@ public class CurryNode extends BaseNode {
 
   private Stateful doCall(
       Function function, CallerInfo callerInfo, Object state, Object[] arguments) {
-    if (preApplicationSchema.getCallStrategy().shouldCallDirect(isTail())) {
-      return directCall.executeCall(function, callerInfo, state, arguments);
-    } else if (isTail()) {
-      throw new TailCallException(function, callerInfo, state, arguments);
-    } else {
-      return loopingCall.executeDispatch(function, callerInfo, state, arguments);
+    switch (getTailStatus()) {
+      case TAIL_DIRECT:
+        return directCall.executeCall(function, callerInfo, state, arguments);
+      case TAIL_LOOP:
+        throw new TailCallException(function, callerInfo, state, arguments);
+      default:
+        return loopingCall.executeDispatch(function, callerInfo, state, arguments);
     }
   }
 }

engine/runtime/src/main/java/org/enso/interpreter/node/callable/dispatch/IndirectCurryNode.java

@@ -6,6 +6,7 @@ import com.oracle.truffle.api.dsl.Specialization;
 import com.oracle.truffle.api.frame.MaterializedFrame;
 import com.oracle.truffle.api.nodes.Node;
 import com.oracle.truffle.api.nodes.NodeInfo;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.callable.ExecuteCallNode;
 import org.enso.interpreter.node.callable.IndirectInvokeCallableNode;
 import org.enso.interpreter.node.callable.InvokeCallableNode;
@@ -36,7 +37,6 @@ public abstract class IndirectCurryNode extends Node {
    * @param arguments the properly ordered arguments to pass to the function.
    * @param oversaturatedArguments any arguments that should be treated as candidates for an
    *     eta-expanded call.
-   * @param originalSchema function schema before the call.
    * @param postApplicationSchema function schema after the call.
    * @param defaultsExecutionMode should default arguments be used for this call.
    * @param argumentsExecutionMode are arguments pre-executed or suspended.
@@ -50,11 +50,10 @@ public abstract class IndirectCurryNode extends Node {
       Object state,
       Object[] arguments,
       Object[] oversaturatedArguments,
-      FunctionSchema originalSchema,
       FunctionSchema postApplicationSchema,
       InvokeCallableNode.DefaultsExecutionMode defaultsExecutionMode,
       InvokeCallableNode.ArgumentsExecutionMode argumentsExecutionMode,
-      boolean isTail);
+      BaseNode.TailStatus isTail);
 
   @Specialization
   Stateful doCurry(
@@ -64,11 +63,10 @@ public abstract class IndirectCurryNode extends Node {
       Object state,
       Object[] arguments,
       Object[] oversaturatedArguments,
-      FunctionSchema preApplicationSchema,
       FunctionSchema postApplicationSchema,
       InvokeCallableNode.DefaultsExecutionMode defaultsExecutionMode,
       InvokeCallableNode.ArgumentsExecutionMode argumentsExecutionMode,
-      boolean isTail,
+      BaseNode.TailStatus isTail,
       @Cached ExecuteCallNode directCall,
       @Cached LoopingCallOptimiserNode loopingCall,
       @Cached IndirectInvokeCallableNode oversaturatedCallableNode) {
@@ -81,7 +79,6 @@ public abstract class IndirectCurryNode extends Node {
                 callerInfo,
                 state,
                 arguments,
-                preApplicationSchema,
                 isTail,
                 directCall,
                 loopingCall);
@@ -128,16 +125,16 @@ public abstract class IndirectCurryNode extends Node {
       CallerInfo callerInfo,
       Object state,
       Object[] arguments,
-      FunctionSchema preApplicationSchema,
-      boolean isTail,
+      BaseNode.TailStatus isTail,
       ExecuteCallNode directCall,
       CallOptimiserNode loopingCall) {
-    if (preApplicationSchema.getCallStrategy().shouldCallDirect(isTail)) {
-      return directCall.executeCall(function, callerInfo, state, arguments);
-    } else if (isTail) {
-      throw new TailCallException(function, callerInfo, state, arguments);
-    } else {
-      return loopingCall.executeDispatch(function, callerInfo, state, arguments);
+    switch (isTail) {
+      case TAIL_DIRECT:
+        return directCall.executeCall(function, callerInfo, state, arguments);
+      case TAIL_LOOP:
+        throw new TailCallException(function, callerInfo, state, arguments);
+      default:
+        return loopingCall.executeDispatch(function, callerInfo, state, arguments);
     }
   }
 }

engine/runtime/src/main/java/org/enso/interpreter/node/callable/dispatch/IndirectInvokeFunctionNode.java

@@ -6,6 +6,7 @@ import com.oracle.truffle.api.dsl.ImportStatic;
 import com.oracle.truffle.api.dsl.Specialization;
 import com.oracle.truffle.api.frame.MaterializedFrame;
 import com.oracle.truffle.api.nodes.Node;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.callable.CaptureCallerInfoNode;
 import org.enso.interpreter.node.callable.InvokeCallableNode;
 import org.enso.interpreter.node.callable.argument.ArgumentSorterNode;
@@ -45,7 +46,7 @@ public abstract class IndirectInvokeFunctionNode extends Node {
       CallArgumentInfo[] schema,
       InvokeCallableNode.DefaultsExecutionMode defaultsExecutionMode,
       InvokeCallableNode.ArgumentsExecutionMode argumentsExecutionMode,
-      boolean isTail);
+      BaseNode.TailStatus isTail);
 
   @Specialization
   Stateful invokeUncached(
@@ -56,7 +57,7 @@ public abstract class IndirectInvokeFunctionNode extends Node {
       CallArgumentInfo[] schema,
       InvokeCallableNode.DefaultsExecutionMode defaultsExecutionMode,
       InvokeCallableNode.ArgumentsExecutionMode argumentsExecutionMode,
-      boolean isTail,
+      BaseNode.TailStatus isTail,
       @Cached IndirectArgumentSorterNode mappingNode,
       @Cached IndirectCurryNode curryNode,
       @Cached CaptureCallerInfoNode captureCallerInfoNode) {
@@ -85,7 +86,6 @@ public abstract class IndirectInvokeFunctionNode extends Node {
         mappedArguments.getState(),
         mappedArguments.getSortedArguments(),
         mappedArguments.getOversaturatedArguments(),
-        function.getSchema(),
         argumentMapping.getPostApplicationSchema(),
         defaultsExecutionMode,
         argumentsExecutionMode,

engine/runtime/src/main/java/org/enso/interpreter/node/callable/dispatch/InvokeFunctionNode.java

@@ -77,7 +77,7 @@ public abstract class InvokeFunctionNode extends BaseNode {
       @Cached("build(cachedSchema, argumentMapping, getArgumentsExecutionMode())")
           ArgumentSorterNode mappingNode,
       @Cached(
-              "build(cachedSchema, argumentMapping, getDefaultsExecutionMode(), getArgumentsExecutionMode(), isTail())")
+              "build(argumentMapping, getDefaultsExecutionMode(), getArgumentsExecutionMode(), getTailStatus())")
           CurryNode curryNode) {
     ArgumentSorterNode.MappedArguments mappedArguments =
         mappingNode.execute(function, state, arguments);
@@ -142,11 +142,10 @@ public abstract class InvokeFunctionNode extends BaseNode {
         mappedArguments.getState(),
         mappedArguments.getSortedArguments(),
         mappedArguments.getOversaturatedArguments(),
-        function.getSchema(),
         argumentMapping.getPostApplicationSchema(),
         defaultsExecutionMode,
         argumentsExecutionMode,
-        isTail());
+        getTailStatus());
   }
 
   /**

engine/runtime/src/main/java/org/enso/interpreter/node/callable/function/CreateFunctionNode.java

@@ -4,7 +4,6 @@ import com.oracle.truffle.api.RootCallTarget;
 import com.oracle.truffle.api.frame.MaterializedFrame;
 import com.oracle.truffle.api.frame.VirtualFrame;
 import com.oracle.truffle.api.nodes.NodeInfo;
-import org.enso.interpreter.node.ClosureRootNode;
 import org.enso.interpreter.node.ExpressionNode;
 import org.enso.interpreter.runtime.callable.argument.ArgumentDefinition;
 import org.enso.interpreter.runtime.callable.function.Function;
@@ -23,7 +22,7 @@ public class CreateFunctionNode extends ExpressionNode {
 
   private CreateFunctionNode(RootCallTarget callTarget, ArgumentDefinition[] args) {
     this.callTarget = callTarget;
-    this.schema = new FunctionSchema(FunctionSchema.CallStrategy.CALL_LOOP, args);
+    this.schema = new FunctionSchema(args);
   }
 
   /**

engine/runtime/src/main/java/org/enso/interpreter/node/callable/thunk/ForceNode.java

@@ -33,7 +33,7 @@ public abstract class ForceNode extends ExpressionNode {
       Thunk thunk,
       @Cached("build()") ThunkExecutorNode thunkExecutorNode) {
     Object state = FrameUtil.getObjectSafe(frame, getStateFrameSlot());
-    Stateful result = thunkExecutorNode.executeThunk(thunk, state, isTail());
+    Stateful result = thunkExecutorNode.executeThunk(thunk, state, getTailStatus());
     frame.setObject(getStateFrameSlot(), result.getState());
     return result.getValue();
   }

engine/runtime/src/main/java/org/enso/interpreter/node/callable/thunk/ThunkExecutorNode.java

@@ -6,6 +6,7 @@ import com.oracle.truffle.api.nodes.DirectCallNode;
 import com.oracle.truffle.api.nodes.IndirectCallNode;
 import com.oracle.truffle.api.nodes.Node;
 import org.enso.interpreter.Constants;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.callable.dispatch.LoopingCallOptimiserNode;
 import org.enso.interpreter.runtime.callable.argument.Thunk;
 import org.enso.interpreter.runtime.callable.function.Function;
@@ -36,7 +37,7 @@ public abstract class ThunkExecutorNode extends Node {
    * @param isTail is the execution happening in a tail-call position
    * @return the return value of this thunk
    */
-  public abstract Stateful executeThunk(Thunk thunk, Object state, boolean isTail);
+  public abstract Stateful executeThunk(Thunk thunk, Object state, BaseNode.TailStatus isTail);
 
   @Specialization(
       guards = "callNode.getCallTarget() == thunk.getCallTarget()",
@@ -44,11 +45,11 @@ public abstract class ThunkExecutorNode extends Node {
   Stateful doCached(
       Thunk thunk,
       Object state,
-      boolean isTail,
+      BaseNode.TailStatus isTail,
       @Cached("create(thunk.getCallTarget())") DirectCallNode callNode,
       @Cached LoopingCallOptimiserNode loopingCallOptimiserNode) {
     CompilerAsserts.partialEvaluationConstant(isTail);
-    if (isTail) {
+    if (isTail != BaseNode.TailStatus.NOT_TAIL) {
       return (Stateful) callNode.call(Function.ArgumentsHelper.buildArguments(thunk, state));
     } else {
       try {
@@ -64,10 +65,10 @@ public abstract class ThunkExecutorNode extends Node {
   Stateful doUncached(
       Thunk thunk,
       Object state,
-      boolean isTail,
+      BaseNode.TailStatus isTail,
       @Cached IndirectCallNode callNode,
       @Cached LoopingCallOptimiserNode loopingCallOptimiserNode) {
-    if (isTail) {
+    if (isTail != BaseNode.TailStatus.NOT_TAIL) {
       return (Stateful)
           callNode.call(
               thunk.getCallTarget(), Function.ArgumentsHelper.buildArguments(thunk, state));

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/bool/IfThenElseNode.java

@@ -4,6 +4,7 @@ import com.oracle.truffle.api.nodes.Node;
 import com.oracle.truffle.api.profiles.ConditionProfile;
 import org.enso.interpreter.dsl.BuiltinMethod;
 import org.enso.interpreter.dsl.MonadicState;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.callable.thunk.ThunkExecutorNode;
 import org.enso.interpreter.runtime.callable.argument.Thunk;
 import org.enso.interpreter.runtime.state.Stateful;
@@ -11,7 +12,6 @@ import org.enso.interpreter.runtime.state.Stateful;
 @BuiltinMethod(
     type = "Boolean",
     name = "if_then_else",
-    alwaysDirect = false,
     description = "Performs the standard if-then-else control flow operation.")
 public class IfThenElseNode extends Node {
   private @Child ThunkExecutorNode leftThunkExecutorNode = ThunkExecutorNode.build();
@@ -20,9 +20,9 @@ public class IfThenElseNode extends Node {
 
   Stateful execute(@MonadicState Object state, boolean _this, Thunk if_true, Thunk if_false) {
     if (condProfile.profile(_this)) {
-      return leftThunkExecutorNode.executeThunk(if_true, state, true);
+      return leftThunkExecutorNode.executeThunk(if_true, state, BaseNode.TailStatus.TAIL_DIRECT);
     } else {
-      return rightThunkExecutorNode.executeThunk(if_false, state, true);
+      return rightThunkExecutorNode.executeThunk(if_false, state, BaseNode.TailStatus.TAIL_DIRECT);
     }
   }
 }

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/bool/IfThenNode.java

@@ -7,6 +7,7 @@ import com.oracle.truffle.api.profiles.ConditionProfile;
 import org.enso.interpreter.Language;
 import org.enso.interpreter.dsl.BuiltinMethod;
 import org.enso.interpreter.dsl.MonadicState;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.callable.thunk.ThunkExecutorNode;
 import org.enso.interpreter.runtime.Context;
 import org.enso.interpreter.runtime.callable.argument.Thunk;
@@ -15,7 +16,6 @@ import org.enso.interpreter.runtime.state.Stateful;
 @BuiltinMethod(
     type = "Boolean",
     name = "if_then",
-    alwaysDirect = false,
     description = "Performs the standard if-then control flow operation.")
 public abstract class IfThenNode extends Node {
   private @Child ThunkExecutorNode leftThunkExecutorNode = ThunkExecutorNode.build();
@@ -31,7 +31,7 @@ public abstract class IfThenNode extends Node {
   Stateful doExecute(
       Object state, boolean _this, Thunk if_true, @CachedContext(Language.class) Context context) {
     if (condProfile.profile(_this)) {
-      return leftThunkExecutorNode.executeThunk(if_true, state, true);
+      return leftThunkExecutorNode.executeThunk(if_true, state, BaseNode.TailStatus.TAIL_DIRECT);
     } else {
       return new Stateful(state, context.getUnit().newInstance());
     }

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/debug/DebugEvalNode.java

@@ -3,6 +3,7 @@ package org.enso.interpreter.node.expression.builtin.debug;
 import com.oracle.truffle.api.nodes.Node;
 import org.enso.interpreter.dsl.BuiltinMethod;
 import org.enso.interpreter.dsl.MonadicState;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.expression.debug.EvalNode;
 import org.enso.interpreter.runtime.callable.CallerInfo;
 import org.enso.interpreter.runtime.data.text.Text;
@@ -12,13 +13,12 @@ import org.enso.interpreter.runtime.state.Stateful;
 @BuiltinMethod(
     type = "Debug",
     name = "eval",
-    description = "Evaluates an expression passed as a Text argument, in the caller frame.",
-    alwaysDirect = false)
+    description = "Evaluates an expression passed as a Text argument, in the caller frame.")
 public class DebugEvalNode extends Node {
   private @Child EvalNode evalNode = EvalNode.build();
 
   DebugEvalNode() {
-    evalNode.markTail();
+    evalNode.setTailStatus(BaseNode.TailStatus.TAIL_DIRECT);
   }
 
   Stateful execute(

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/error/CatchErrorNode.java

@@ -5,6 +5,7 @@ import com.oracle.truffle.api.nodes.Node;
 import com.oracle.truffle.api.profiles.ConditionProfile;
 import org.enso.interpreter.dsl.BuiltinMethod;
 import org.enso.interpreter.dsl.MonadicState;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.callable.InvokeCallableNode;
 import org.enso.interpreter.runtime.callable.argument.CallArgumentInfo;
 import org.enso.interpreter.runtime.state.Stateful;
@@ -14,8 +15,7 @@ import org.enso.interpreter.runtime.type.TypesGen;
     type = "Any",
     name = "catch",
     description =
-        "If called on an error, executes the provided handler on the error's payload. Otherwise acts as identity.",
-    alwaysDirect = false)
+        "If called on an error, executes the provided handler on the error's payload. Otherwise acts as identity.")
 public class CatchErrorNode extends Node {
   private @Child InvokeCallableNode invokeCallableNode;
   private final ConditionProfile executionProfile = ConditionProfile.createCountingProfile();
@@ -26,7 +26,7 @@ public class CatchErrorNode extends Node {
             new CallArgumentInfo[] {new CallArgumentInfo()},
             InvokeCallableNode.DefaultsExecutionMode.EXECUTE,
             InvokeCallableNode.ArgumentsExecutionMode.PRE_EXECUTED);
-    this.invokeCallableNode.markTail();
+    this.invokeCallableNode.setTailStatus(BaseNode.TailStatus.TAIL_DIRECT);
   }
 
   Stateful execute(VirtualFrame frame, @MonadicState Object state, Object _this, Object handler) {

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/error/CatchPanicNode.java

@@ -7,6 +7,7 @@ import com.oracle.truffle.api.nodes.Node;
 import org.enso.interpreter.Language;
 import org.enso.interpreter.dsl.BuiltinMethod;
 import org.enso.interpreter.dsl.MonadicState;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.callable.thunk.ThunkExecutorNode;
 import org.enso.interpreter.runtime.Context;
 import org.enso.interpreter.runtime.callable.argument.Thunk;
@@ -34,7 +35,7 @@ public abstract class CatchPanicNode extends Node {
       Thunk action,
       @CachedContext(Language.class) Context ctx) {
     try {
-      return thunkExecutorNode.executeThunk(action, state, false);
+      return thunkExecutorNode.executeThunk(action, state, BaseNode.TailStatus.NOT_TAIL);
     } catch (PanicException e) {
       return new Stateful(state, new RuntimeError(e.getExceptionObject()));
     } catch (Throwable e) {

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/function/ApplicationOperator.java

@@ -4,6 +4,7 @@ import com.oracle.truffle.api.frame.VirtualFrame;
 import com.oracle.truffle.api.nodes.Node;
 import org.enso.interpreter.dsl.BuiltinMethod;
 import org.enso.interpreter.dsl.MonadicState;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.callable.InvokeCallableNode;
 import org.enso.interpreter.runtime.callable.argument.CallArgumentInfo;
 import org.enso.interpreter.runtime.callable.argument.Thunk;
@@ -13,8 +14,7 @@ import org.enso.interpreter.runtime.state.Stateful;
 @BuiltinMethod(
     type = "Function",
     name = "<|",
-    description = "Takes a function and an argument and applies the function to the argument.",
-    alwaysDirect = false)
+    description = "Takes a function and an argument and applies the function to the argument.")
 public class ApplicationOperator extends Node {
   private @Child InvokeCallableNode invokeCallableNode;
 
@@ -24,7 +24,7 @@ public class ApplicationOperator extends Node {
             new CallArgumentInfo[] {new CallArgumentInfo()},
             InvokeCallableNode.DefaultsExecutionMode.EXECUTE,
             InvokeCallableNode.ArgumentsExecutionMode.EXECUTE);
-    invokeCallableNode.markTail();
+    invokeCallableNode.setTailStatus(BaseNode.TailStatus.TAIL_DIRECT);
   }
 
   Stateful execute(VirtualFrame frame, @MonadicState Object state, Function _this, Thunk argument) {

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/function/ExplicitCallFunctionNode.java

@@ -4,6 +4,7 @@ import com.oracle.truffle.api.frame.VirtualFrame;
 import com.oracle.truffle.api.nodes.Node;
 import org.enso.interpreter.dsl.BuiltinMethod;
 import org.enso.interpreter.dsl.MonadicState;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.callable.InvokeCallableNode;
 import org.enso.interpreter.runtime.callable.argument.CallArgumentInfo;
 import org.enso.interpreter.runtime.callable.function.Function;
@@ -12,8 +13,7 @@ import org.enso.interpreter.runtime.state.Stateful;
 @BuiltinMethod(
     type = "Function",
     name = "call",
-    description = "Allows function calls to be made explicitly",
-    alwaysDirect = false)
+    description = "Allows function calls to be made explicitly")
 public class ExplicitCallFunctionNode extends Node {
   private @Child InvokeCallableNode invokeCallableNode;
 
@@ -23,7 +23,7 @@ public class ExplicitCallFunctionNode extends Node {
             new CallArgumentInfo[0],
             InvokeCallableNode.DefaultsExecutionMode.EXECUTE,
             InvokeCallableNode.ArgumentsExecutionMode.PRE_EXECUTED);
-    invokeCallableNode.markTail();
+    invokeCallableNode.setTailStatus(BaseNode.TailStatus.TAIL_DIRECT);
   }
 
   Stateful execute(VirtualFrame frame, @MonadicState Object state, Function _this) {

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/interop/syntax/ArrayLengthNode.java

@@ -1,25 +1,12 @@
 package org.enso.interpreter.node.expression.builtin.interop.syntax;
 
-import com.oracle.truffle.api.frame.VirtualFrame;
-import com.oracle.truffle.api.interop.ArityException;
 import com.oracle.truffle.api.interop.InteropLibrary;
 import com.oracle.truffle.api.interop.UnsupportedMessageException;
-import com.oracle.truffle.api.interop.UnsupportedTypeException;
-import com.oracle.truffle.api.library.CachedLibrary;
 import com.oracle.truffle.api.nodes.Node;
-import com.oracle.truffle.api.nodes.NodeInfo;
-import com.oracle.truffle.api.nodes.UnexpectedResultException;
 import com.oracle.truffle.api.profiles.BranchProfile;
 import org.enso.interpreter.Constants;
-import org.enso.interpreter.Language;
 import org.enso.interpreter.dsl.BuiltinMethod;
-import org.enso.interpreter.node.expression.builtin.BuiltinRootNode;
-import org.enso.interpreter.runtime.callable.argument.ArgumentDefinition;
-import org.enso.interpreter.runtime.callable.function.Function;
-import org.enso.interpreter.runtime.callable.function.FunctionSchema.CallStrategy;
 import org.enso.interpreter.runtime.error.PanicException;
-import org.enso.interpreter.runtime.state.Stateful;
-import org.enso.interpreter.runtime.type.TypesGen;
 
 @BuiltinMethod(
     type = "Any",

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/interop/syntax/ConstructorDispatchNode.java

@@ -13,7 +13,6 @@ import org.enso.interpreter.Language;
 import org.enso.interpreter.node.expression.builtin.BuiltinRootNode;
 import org.enso.interpreter.runtime.callable.argument.ArgumentDefinition;
 import org.enso.interpreter.runtime.callable.function.Function;
-import org.enso.interpreter.runtime.callable.function.FunctionSchema.CallStrategy;
 import org.enso.interpreter.runtime.error.PanicException;
 import org.enso.interpreter.runtime.state.Stateful;
 import org.enso.interpreter.runtime.type.TypesGen;
@@ -37,7 +36,6 @@ public class ConstructorDispatchNode extends BuiltinRootNode {
   public static Function makeFunction(Language language) {
     return Function.fromBuiltinRootNode(
         new ConstructorDispatchNode(language),
-        CallStrategy.ALWAYS_DIRECT,
         new ArgumentDefinition(0, "this", ArgumentDefinition.ExecutionMode.EXECUTE),
         new ArgumentDefinition(1, "arguments", ArgumentDefinition.ExecutionMode.EXECUTE));
   }

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/resource/BracketNode.java

@@ -5,6 +5,7 @@ import com.oracle.truffle.api.frame.VirtualFrame;
 import com.oracle.truffle.api.nodes.Node;
 import org.enso.interpreter.dsl.BuiltinMethod;
 import org.enso.interpreter.dsl.MonadicState;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.callable.InvokeCallableNode;
 import org.enso.interpreter.node.callable.thunk.ThunkExecutorNode;
 import org.enso.interpreter.runtime.callable.argument.CallArgumentInfo;
@@ -61,7 +62,8 @@ public abstract class BracketNode extends Node {
       Thunk constructor,
       Object destructor,
       Object action) {
-    Stateful resourceStateful = invokeConstructorNode.executeThunk(constructor, state, false);
+    Stateful resourceStateful =
+        invokeConstructorNode.executeThunk(constructor, state, BaseNode.TailStatus.NOT_TAIL);
     Object resource = resourceStateful.getValue();
     state = resourceStateful.getState();
     try {

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/runtime/NoInlineNode.java

@@ -4,6 +4,7 @@ import com.oracle.truffle.api.CompilerDirectives;
 import com.oracle.truffle.api.nodes.Node;
 import org.enso.interpreter.dsl.BuiltinMethod;
 import org.enso.interpreter.dsl.MonadicState;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.callable.thunk.ThunkExecutorNode;
 import org.enso.interpreter.runtime.callable.argument.Thunk;
 import org.enso.interpreter.runtime.state.Stateful;
@@ -17,6 +18,6 @@ public class NoInlineNode extends Node {
 
   @CompilerDirectives.TruffleBoundary
   Stateful execute(@MonadicState Object state, Object _this, Thunk action) {
-    return thunkExecutorNode.executeThunk(action, state, false);
+    return thunkExecutorNode.executeThunk(action, state, BaseNode.TailStatus.NOT_TAIL);
   }
 }

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/state/RunStateNode.java

@@ -7,6 +7,7 @@ import com.oracle.truffle.api.dsl.Specialization;
 import com.oracle.truffle.api.nodes.Node;
 import org.enso.interpreter.dsl.BuiltinMethod;
 import org.enso.interpreter.dsl.MonadicState;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.callable.thunk.ThunkExecutorNode;
 import org.enso.interpreter.runtime.callable.argument.Thunk;
 import org.enso.interpreter.runtime.state.data.EmptyMap;
@@ -34,7 +35,10 @@ public abstract class RunStateNode extends Node {
   Stateful doEmpty(
       EmptyMap state, Object _this, Object key, Object local_state, Thunk computation) {
     SingletonMap localStateMap = new SingletonMap(key, local_state);
-    Object result = thunkExecutorNode.executeThunk(computation, localStateMap, false).getValue();
+    Object result =
+        thunkExecutorNode
+            .executeThunk(computation, localStateMap, BaseNode.TailStatus.NOT_TAIL)
+            .getValue();
     return new Stateful(state, result);
   }
 
@@ -42,7 +46,9 @@ public abstract class RunStateNode extends Node {
   Stateful doSingletonSameKey(
       SingletonMap state, Object _this, Object key, Object local_state, Thunk computation) {
     SingletonMap localStateContainer = new SingletonMap(state.getKey(), local_state);
-    Stateful res = thunkExecutorNode.executeThunk(computation, localStateContainer, false);
+    Stateful res =
+        thunkExecutorNode.executeThunk(
+            computation, localStateContainer, BaseNode.TailStatus.NOT_TAIL);
     return new Stateful(state, res.getValue());
   }
 
@@ -63,7 +69,8 @@ public abstract class RunStateNode extends Node {
       @Cached(value = "buildSmallKeys(cachedNewKey, cachedOldKey)", dimensions = 1)
           Object[] newKeys) {
     SmallMap localStateMap = new SmallMap(newKeys, new Object[] {local_state, state.getValue()});
-    Stateful res = thunkExecutorNode.executeThunk(computation, localStateMap, false);
+    Stateful res =
+        thunkExecutorNode.executeThunk(computation, localStateMap, BaseNode.TailStatus.NOT_TAIL);
     Object newStateVal = ((SmallMap) res.getState()).getValues()[1];
     return new Stateful(new SingletonMap(cachedOldKey, newStateVal), res.getValue());
   }
@@ -103,7 +110,8 @@ public abstract class RunStateNode extends Node {
     System.arraycopy(state.getValues(), 0, newValues, 1, cachedOldKeys.length);
     newValues[0] = local_state;
     SmallMap localStateMap = new SmallMap(newKeys, newValues);
-    Stateful res = thunkExecutorNode.executeThunk(computation, localStateMap, false);
+    Stateful res =
+        thunkExecutorNode.executeThunk(computation, localStateMap, BaseNode.TailStatus.NOT_TAIL);
     SmallMap resultStateMap = (SmallMap) res.getState();
     Object[] resultValues = new Object[cachedOldKeys.length];
     System.arraycopy(resultStateMap.getValues(), 1, resultValues, 0, cachedOldKeys.length);
@@ -125,7 +133,8 @@ public abstract class RunStateNode extends Node {
     System.arraycopy(state.getValues(), 0, newValues, 0, cachedOldKeys.length);
     newValues[index] = local_state;
     SmallMap localStateMap = new SmallMap(cachedOldKeys, newValues);
-    Stateful res = thunkExecutorNode.executeThunk(computation, localStateMap, false);
+    Stateful res =
+        thunkExecutorNode.executeThunk(computation, localStateMap, BaseNode.TailStatus.NOT_TAIL);
     SmallMap resultStateMap = (SmallMap) res.getState();
     Object[] resultValues = new Object[cachedOldKeys.length];
     System.arraycopy(resultStateMap.getValues(), 0, resultValues, 0, cachedOldKeys.length);

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/thread/WithInterruptHandlerNode.java

@@ -3,6 +3,7 @@ package org.enso.interpreter.node.expression.builtin.thread;
 import com.oracle.truffle.api.nodes.Node;
 import org.enso.interpreter.dsl.BuiltinMethod;
 import org.enso.interpreter.dsl.MonadicState;
+import org.enso.interpreter.node.BaseNode;
 import org.enso.interpreter.node.callable.thunk.ThunkExecutorNode;
 import org.enso.interpreter.runtime.callable.argument.Thunk;
 import org.enso.interpreter.runtime.control.ThreadInterruptedException;
@@ -16,11 +17,12 @@ public class WithInterruptHandlerNode extends Node {
   private @Child ThunkExecutorNode actExecutorNode = ThunkExecutorNode.build();
   private @Child ThunkExecutorNode handlerExecutorNode = ThunkExecutorNode.build();
 
-  Stateful execute(@MonadicState Object state, Object _this, Thunk action, Thunk interrupt_handler) {
+  Stateful execute(
+      @MonadicState Object state, Object _this, Thunk action, Thunk interrupt_handler) {
     try {
-      return actExecutorNode.executeThunk(action, state, false);
+      return actExecutorNode.executeThunk(action, state, BaseNode.TailStatus.NOT_TAIL);
     } catch (ThreadInterruptedException e) {
-      handlerExecutorNode.executeThunk(interrupt_handler, state, false);
+      handlerExecutorNode.executeThunk(interrupt_handler, state, BaseNode.TailStatus.NOT_TAIL);
       throw e;
     }
   }

engine/runtime/src/main/java/org/enso/interpreter/node/expression/debug/EvalNode.java

@@ -62,7 +62,7 @@ public abstract class EvalNode extends BaseNode {
 
   RootCallTarget parseExpression(LocalScope scope, ModuleScope moduleScope, String expression) {
     LocalScope localScope = scope.createChild();
-    InlineContext inlineContext = InlineContext.fromJava(localScope, moduleScope, isTail());
+    InlineContext inlineContext = InlineContext.fromJava(localScope, moduleScope, getTailStatus());
     ExpressionNode expr =
         lookupContextReference(Language.class)
             .get()
@@ -107,7 +107,7 @@ public abstract class EvalNode extends BaseNode {
           RootCallTarget cachedCallTarget,
       @Cached("build()") ThunkExecutorNode thunkExecutorNode) {
     Thunk thunk = new Thunk(cachedCallTarget, callerInfo.getFrame());
-    return thunkExecutorNode.executeThunk(thunk, state, isTail());
+    return thunkExecutorNode.executeThunk(thunk, state, getTailStatus());
   }
 
   @Specialization
@@ -123,6 +123,6 @@ public abstract class EvalNode extends BaseNode {
             callerInfo.getModuleScope(),
             toJavaStringNode.execute(expression));
     Thunk thunk = new Thunk(callTarget, callerInfo.getFrame());
-    return thunkExecutorNode.executeThunk(thunk, state, isTail());
+    return thunkExecutorNode.executeThunk(thunk, state, getTailStatus());
   }
 }

engine/runtime/src/main/java/org/enso/interpreter/runtime/builtin/Polyglot.java

@@ -5,7 +5,6 @@ import com.oracle.truffle.api.Truffle;
 import org.enso.interpreter.Language;
 import org.enso.interpreter.node.expression.builtin.interop.generic.*;
 import org.enso.interpreter.node.expression.builtin.interop.syntax.*;
-import org.enso.interpreter.node.expression.builtin.interop.syntax.GetArrayElementMethodGen;
 import org.enso.interpreter.runtime.callable.UnresolvedSymbol;
 import org.enso.interpreter.runtime.callable.argument.ArgumentDefinition;
 import org.enso.interpreter.runtime.callable.argument.CallArgumentInfo;
@@ -36,7 +35,6 @@ public class Polyglot {
     interopDispatchRoot = Truffle.getRuntime().createCallTarget(MethodDispatchNode.build(language));
     interopDispatchSchema =
         new FunctionSchema(
-            FunctionSchema.CallStrategy.ALWAYS_DIRECT,
             FunctionSchema.CallerFrameAccess.NONE,
             new ArgumentDefinition[] {
               new ArgumentDefinition(1, "this", ArgumentDefinition.ExecutionMode.EXECUTE),

engine/runtime/src/main/java/org/enso/interpreter/runtime/callable/argument/CallArgumentInfo.java

@@ -3,10 +3,11 @@ package org.enso.interpreter.runtime.callable.argument;
 import com.oracle.truffle.api.CompilerDirectives;
 import com.oracle.truffle.api.CompilerDirectives.CompilationFinal;
 import com.oracle.truffle.api.nodes.ExplodeLoop;
+import org.enso.interpreter.runtime.callable.function.FunctionSchema;
+
 import java.util.OptionalInt;
 import java.util.function.Predicate;
 import java.util.stream.IntStream;
-import org.enso.interpreter.runtime.callable.function.FunctionSchema;
 
 /**
  * Tracks simple information about call-site arguments, used to make processing of caller argument
@@ -219,7 +220,6 @@ public class CallArgumentInfo {
           newOversaturatedArgInfo.length);
 
       return new FunctionSchema(
-          originalSchema.getCallStrategy(),
           originalSchema.getCallerFrameAccess(),
           definitions,
           argumentUsed,

engine/runtime/src/main/java/org/enso/interpreter/runtime/callable/atom/AtomConstructor.java

@@ -75,8 +75,7 @@ public class AtomConstructor implements TruffleObject {
     ExpressionNode instantiateNode = InstantiateNode.build(this, argumentReaders);
     RootNode rootNode = InstantiateAtomNode.build(null, name, instantiateNode);
     RootCallTarget callTarget = Truffle.getRuntime().createCallTarget(rootNode);
-    return new Function(
-        callTarget, null, new FunctionSchema(FunctionSchema.CallStrategy.ALWAYS_DIRECT, args));
+    return new Function(callTarget, null, new FunctionSchema(args));
   }
 
   private void generateMethods(ArgumentDefinition[] args) {
@@ -94,7 +93,6 @@ public class AtomConstructor implements TruffleObject {
             callTarget,
             null,
             new FunctionSchema(
-                FunctionSchema.CallStrategy.ALWAYS_DIRECT,
                 new ArgumentDefinition(0, "this", ArgumentDefinition.ExecutionMode.EXECUTE)));
     definitionScope.registerMethod(
         definitionScope.getAssociatedType(), this.name.toLowerCase(), function);
@@ -107,7 +105,6 @@ public class AtomConstructor implements TruffleObject {
         callTarget,
         null,
         new FunctionSchema(
-            FunctionSchema.CallStrategy.ALWAYS_DIRECT,
             new ArgumentDefinition(0, "this", ArgumentDefinition.ExecutionMode.EXECUTE)));
   }
 

engine/runtime/src/main/java/org/enso/interpreter/runtime/callable/function/Function.java

@@ -80,14 +80,13 @@ public final class Function implements TruffleObject {
    * Creates a Function object from a {@link BuiltinRootNode} and argument definitions.
    *
    * @param node the {@link RootNode} for the function logic
-   * @param callStrategy the {@link FunctionSchema.CallStrategy} to use for this function
    * @param args argument definitons
    * @return a Function object with specified behavior and arguments
    */
   public static Function fromBuiltinRootNode(
-      BuiltinRootNode node, FunctionSchema.CallStrategy callStrategy, ArgumentDefinition... args) {
+      BuiltinRootNode node, ArgumentDefinition... args) {
     RootCallTarget callTarget = Truffle.getRuntime().createCallTarget(node);
-    FunctionSchema schema = new FunctionSchema(callStrategy, args);
+    FunctionSchema schema = new FunctionSchema(args);
     return new Function(callTarget, null, schema);
   }
 
@@ -98,15 +97,14 @@ public final class Function implements TruffleObject {
    * will be non-null.
    *
    * @param node the {@link RootNode} for the function logic
-   * @param callStrategy the {@link FunctionSchema.CallStrategy} to use for this function
    * @param args argument definitons
    * @return a Function object with specified behavior and arguments
    */
   public static Function fromBuiltinRootNodeWithCallerFrameAccess(
-      BuiltinRootNode node, FunctionSchema.CallStrategy callStrategy, ArgumentDefinition... args) {
+      BuiltinRootNode node, ArgumentDefinition... args) {
     RootCallTarget callTarget = Truffle.getRuntime().createCallTarget(node);
     FunctionSchema schema =
-        new FunctionSchema(callStrategy, FunctionSchema.CallerFrameAccess.FULL, args);
+        new FunctionSchema(FunctionSchema.CallerFrameAccess.FULL, args);
     return new Function(callTarget, null, schema);
   }
 
@@ -129,15 +127,6 @@ public final class Function implements TruffleObject {
     return getCallTarget().getRootNode().getSourceSection();
   }
 
-  /**
-   * Gets the call strategy that should be used for this function.
-   *
-   * @return this function's call strategy
-   */
-  public FunctionSchema.CallStrategy getCallStrategy() {
-    return getSchema().getCallStrategy();
-  }
-
   /**
    * Gets the function's scope.
    *

engine/runtime/src/main/java/org/enso/interpreter/runtime/callable/function/FunctionSchema.java

@@ -11,36 +11,6 @@ import org.enso.interpreter.runtime.callable.argument.CallArgumentInfo;
  * arguments positions.
  */
 public class FunctionSchema {
-
-  /**
-   * Denotes the call strategy that should be used whenever a function with this schema is called.
-   *
-   * <p>For builtin functions, the algorithm for choosing the proper {@link CallStrategy} is as
-   * follows: if the node executes user-provided code ({@link
-   * org.enso.interpreter.runtime.callable.argument.Thunk} or a {@link Function}) using the Tail
-   * Call Optimization machinery (i.e. marking the execution node as tail position), the right
-   * choice is {@code DIRECT_WHEN_TAIL}. Otherwise {@code ALWAYS_DIRECT} should be chosen.
-   */
-  public enum CallStrategy {
-
-    /** Always call the function directly. */
-    ALWAYS_DIRECT,
-    /** Call the function directly when said function is in tail call position. */
-    DIRECT_WHEN_TAIL,
-    /** Always call the function using standard tail call machinery. */
-    CALL_LOOP;
-
-    /**
-     * Should this function be called directly in the given position?
-     *
-     * @param isTail is this a tail position?
-     * @return {@code true} if the function should be called directly, {@code false} otherwise
-     */
-    public boolean shouldCallDirect(boolean isTail) {
-      return this == ALWAYS_DIRECT || (this == DIRECT_WHEN_TAIL && isTail);
-    }
-  }
-
   /** Denotes the caller frame access functions with this schema require to run properly. */
   public enum CallerFrameAccess {
     /** Requires full access to the (materialized) caller frame. */
@@ -62,7 +32,6 @@ public class FunctionSchema {
   private final @CompilationFinal(dimensions = 1) ArgumentDefinition[] argumentInfos;
   private final @CompilationFinal(dimensions = 1) boolean[] hasPreApplied;
   private final @CompilationFinal(dimensions = 1) CallArgumentInfo[] oversaturatedArguments;
-  private final CallStrategy callStrategy;
   private final boolean hasAnyPreApplied;
   private final boolean hasOversaturatedArguments;
   private final CallerFrameAccess callerFrameAccess;
@@ -70,7 +39,6 @@ public class FunctionSchema {
   /**
    * Creates an {@link FunctionSchema} instance.
    *
-   * @param callStrategy the call strategy to use for functions having this schema
    * @param callerFrameAccess the declaration of whether access to caller frame is required for this
    *     function
    * @param argumentInfos Definition site arguments information
@@ -80,12 +48,10 @@ public class FunctionSchema {
    *     this function so far
    */
   public FunctionSchema(
-      CallStrategy callStrategy,
       CallerFrameAccess callerFrameAccess,
       ArgumentDefinition[] argumentInfos,
       boolean[] hasPreApplied,
       CallArgumentInfo[] oversaturatedArguments) {
-    this.callStrategy = callStrategy;
     this.argumentInfos = argumentInfos;
     this.oversaturatedArguments = oversaturatedArguments;
     this.hasPreApplied = hasPreApplied;
@@ -106,16 +72,13 @@ public class FunctionSchema {
    * Creates an {@link FunctionSchema} instance assuming the function has no partially applied
    * arguments.
    *
-   * @param callStrategy the call strategy to use for this function
    * @param callerFrameAccess the declaration of need to access the caller frame from the function
    * @param argumentInfos Definition site arguments information
    */
   public FunctionSchema(
-      CallStrategy callStrategy,
       CallerFrameAccess callerFrameAccess,
       ArgumentDefinition... argumentInfos) {
     this(
-        callStrategy,
         callerFrameAccess,
         argumentInfos,
         new boolean[argumentInfos.length],
@@ -128,11 +91,10 @@ public class FunctionSchema {
    *
    * <p>Caller frame access is assumed to be {@link CallerFrameAccess#NONE}.
    *
-   * @param callStrategy the call strategy to use for this function
    * @param argumentInfos Definition site arguments information
    */
-  public FunctionSchema(CallStrategy callStrategy, ArgumentDefinition... argumentInfos) {
-    this(callStrategy, CallerFrameAccess.NONE, argumentInfos);
+  public FunctionSchema(ArgumentDefinition... argumentInfos) {
+    this(CallerFrameAccess.NONE, argumentInfos);
   }
 
   /**
@@ -222,15 +184,6 @@ public class FunctionSchema {
     return oversaturatedArguments;
   }
 
-  /**
-   * Returns the call strategy to use for functions with this schema.
-   *
-   * @return the call strategy to use
-   */
-  public CallStrategy getCallStrategy() {
-    return callStrategy;
-  }
-
   /**
    * Returns the caller frame access declaration for this function.
    *

engine/runtime/src/main/scala/org/enso/compiler/Passes.scala

@@ -43,6 +43,7 @@ class Passes(passes: Option[List[PassGroup]] = None) {
       IgnoredBindings,
       TypeFunctions,
       TypeSignatures,
+      Annotations,
       AliasAnalysis,
       UppercaseNames,
       VectorLiterals,

engine/runtime/src/main/scala/org/enso/compiler/codegen/AstToIr.scala

@@ -834,6 +834,8 @@ object AstToIr {
         } else {
           buildName(identifier)
         }
+      case AST.Ident.Annotation(name) =>
+        Name.Annotation(name, getIdentifiedLocation(identifier))
       case AST.Ident.Cons(_) =>
         buildName(identifier)
       case AST.Ident.Blank(_) =>

engine/runtime/src/main/scala/org/enso/compiler/codegen/IrToTruffle.scala

@@ -19,6 +19,7 @@ import org.enso.compiler.pass.analyse.{
 }
 import org.enso.compiler.pass.optimise.ApplicationSaturation
 import org.enso.compiler.pass.resolve.{
+  Annotations,
   MethodDefinitions,
   Patterns,
   UppercaseNames
@@ -51,6 +52,7 @@ import org.enso.interpreter.node.expression.literal.{
 }
 import org.enso.interpreter.node.scope.{AssignmentNode, ReadLocalVariableNode}
 import org.enso.interpreter.node.{
+  BaseNode,
   ClosureRootNode,
   MethodRootNode,
   ExpressionNode => RuntimeExpression
@@ -270,10 +272,7 @@ class IrToTruffle(
               new RuntimeFunction(
                 callTarget,
                 null,
-                new FunctionSchema(
-                  FunctionSchema.CallStrategy.CALL_LOOP,
-                  arguments: _*
-                )
+                new FunctionSchema(arguments: _*)
               )
             case _ =>
               throw new CompilerError(
@@ -303,6 +302,23 @@ class IrToTruffle(
       .getOrElse(source.createUnavailableSection())
   }
 
+  private def getTailStatus(
+    expression: IR.Expression
+  ): BaseNode.TailStatus = {
+    val isTailPosition =
+      expression.getMetadata(TailCall).contains(TailCall.TailPosition.Tail)
+    val isTailAnnotated = expression.getMetadata(Annotations).isDefined
+    if (isTailPosition) {
+      if (isTailAnnotated) {
+        BaseNode.TailStatus.TAIL_LOOP
+      } else {
+        BaseNode.TailStatus.TAIL_DIRECT
+      }
+    } else {
+      BaseNode.TailStatus.NOT_TAIL
+    }
+  }
+
   /** Sets the source section for a given expression node to the provided
     * location.
     *
@@ -333,7 +349,6 @@ class IrToTruffle(
       new EnsoProjectNode(language, context, pkg)
     )
     val schema = new FunctionSchema(
-      FunctionSchema.CallStrategy.ALWAYS_DIRECT,
       new ArgumentDefinition(
         0,
         "this",
@@ -352,7 +367,6 @@ class IrToTruffle(
         ),
         null,
         new FunctionSchema(
-          FunctionSchema.CallStrategy.ALWAYS_DIRECT,
           new ArgumentDefinition(
             0,
             "this",
@@ -460,11 +474,6 @@ class IrToTruffle(
       * @return a truffle expression that represents the same program as `ir`
       */
     def run(ir: IR.Expression): RuntimeExpression = {
-      val tailMeta = ir.unsafeGetMetadata(
-        TailCall,
-        "Missing tail call information on method."
-      )
-
       val runtimeExpression = ir match {
         case block: IR.Expression.Block     => processBlock(block)
         case literal: IR.Literal            => processLiteral(literal)
@@ -489,7 +498,7 @@ class IrToTruffle(
           )
       }
 
-      runtimeExpression.setTail(tailMeta)
+      runtimeExpression.setTailStatus(getTailStatus(ir))
       runtimeExpression
     }
 
@@ -623,11 +632,6 @@ class IrToTruffle(
         )
         .unsafeAs[AliasAnalysis.Info.Scope.Child]
 
-      val branchIsTail = branch.unsafeGetMetadata(
-        TailCall,
-        "Case branch is missing tail position information."
-      )
-
       val childProcessor = this.createChild("case_branch", scopeInfo.scope)
 
       branch.pattern match {
@@ -641,7 +645,6 @@ class IrToTruffle(
           )
 
           val branchNode = CatchAllBranchNode.build(branchCodeNode)
-          branchNode.setTail(branchIsTail)
 
           Right(branchNode)
         case cons @ Pattern.Constructor(constructor, _, _, _, _) =>
@@ -707,7 +710,6 @@ class IrToTruffle(
               } else {
                 ConstructorBranchNode.build(atomCons, branchCodeNode)
               }
-            branchNode.setTail(branchIsTail)
 
             branchNode
           }
@@ -861,6 +863,10 @@ class IrToTruffle(
               passData
             )
           )
+        case _: IR.Name.Annotation =>
+          throw new CompilerError(
+            "Annotation should not be present at codegen time."
+          )
         case _: IR.Name.Blank =>
           throw new CompilerError(
             "Blanks should not be present at codegen time."
@@ -997,15 +1003,9 @@ class IrToTruffle(
         } else seenArgNames.add(argName)
       }
 
-      val bodyIsTail = body.unsafeGetMetadata(
-        TailCall,
-        "Function body missing tail call information."
-      )
-
       val bodyExpr = this.run(body)
 
       val fnBodyNode = BlockNode.build(argExpressions.toArray, bodyExpr)
-      fnBodyNode.setTail(bodyIsTail)
       (fnBodyNode, argDefinitions)
     }
 
@@ -1188,12 +1188,7 @@ class IrToTruffle(
           val result = if (!shouldSuspend) {
             argumentExpression
           } else {
-            val argExpressionIsTail = value.unsafeGetMetadata(
-              TailCall,
-              "Argument with missing tail call information."
-            )
-
-            argumentExpression.setTail(argExpressionIsTail)
+            argumentExpression.setTailStatus(getTailStatus(value))
 
             val displayName =
               s"argument<${name.map(_.name).getOrElse(String.valueOf(position))}>"

engine/runtime/src/main/scala/org/enso/compiler/context/InlineContext.scala

@@ -1,6 +1,7 @@
 package org.enso.compiler.context
 
 import org.enso.compiler.pass.PassConfiguration
+import org.enso.interpreter.node.BaseNode.TailStatus
 import org.enso.interpreter.runtime.scope.{LocalScope, ModuleScope}
 import org.enso.interpreter.runtime.Module
 
@@ -35,12 +36,12 @@ object InlineContext {
   def fromJava(
     localScope: LocalScope,
     moduleScope: ModuleScope,
-    isInTailPosition: Boolean
+    isInTailPosition: TailStatus
   ): InlineContext = {
     InlineContext(
       localScope       = Option(localScope),
       module           = moduleScope.getModule,
-      isInTailPosition = Option(isInTailPosition)
+      isInTailPosition = Option(isInTailPosition != TailStatus.NOT_TAIL)
     )
   }
 }

engine/runtime/src/main/scala/org/enso/compiler/core/IR.scala

@@ -2084,6 +2084,82 @@ object IR {
       override def showCode(indent: Int): String = name
     }
 
+    /** The representation of an annotation name.
+      *
+      * @param name the annotation text of the name
+      * @param location the source location that the node corresponds to
+      * @param passData the pass metadata associated with this node
+      * @param diagnostics compiler diagnostics for this node
+      */
+    sealed case class Annotation(
+      override val name: String,
+      override val location: Option[IdentifiedLocation],
+      override val passData: MetadataStorage      = MetadataStorage(),
+      override val diagnostics: DiagnosticStorage = DiagnosticStorage()
+    ) extends Name {
+      override protected var id: Identifier = randomId
+
+      /** Creates a copy of `this`.
+        *
+        * @param name the annotation text of the name
+        * @param location the source location that the node corresponds to
+        * @param passData the pass metadata associated with this node
+        * @param diagnostics compiler diagnostics for this node
+        * @param id the identifier for the new node
+        * @return a copy of `this`, updated with the specified values
+        */
+      def copy(
+        name: String                         = name,
+        location: Option[IdentifiedLocation] = location,
+        passData: MetadataStorage            = passData,
+        diagnostics: DiagnosticStorage       = diagnostics,
+        id: Identifier                       = id
+      ): Annotation = {
+        val res = Annotation(name, location, passData, diagnostics)
+        res.id = id
+        res
+      }
+
+      override def duplicate(
+        keepLocations: Boolean   = true,
+        keepMetadata: Boolean    = true,
+        keepDiagnostics: Boolean = true
+      ): Annotation =
+        copy(
+          location = if (keepLocations) location else None,
+          passData =
+            if (keepMetadata) passData.duplicate else MetadataStorage(),
+          diagnostics =
+            if (keepDiagnostics) diagnostics.copy else DiagnosticStorage(),
+          id = randomId
+        )
+
+      override def setLocation(
+        location: Option[IdentifiedLocation]
+      ): Annotation =
+        copy(location = location)
+
+      override def mapExpressions(fn: Expression => Expression): Annotation =
+        this
+
+      override def toString: String =
+        s"""
+           |IR.Name.Annotation(
+           |name = $name,
+           |location = $location,
+           |passData = ${this.showPassData},
+           |diagnostics = $diagnostics,
+           |id = $id
+           |)
+           |""".toSingleLine
+
+      override def children: List[IR] = List()
+
+      override def isReferent: Boolean = false
+
+      override def showCode(indent: Int): String = name
+    }
+
     /** A representation of the name `this`, used to refer to the current type.
       *
       * @param location the source location that the node corresponds to
@@ -5196,6 +5272,17 @@ object IR {
       }
     }
 
+    /**
+      * A warning about a `@Tail_Call` annotation placed in a non-tail
+      * position.
+      * @param location the location of the annotated application
+      */
+    case class WrongTco(override val location: Option[IdentifiedLocation])
+        extends Warning {
+      override def message: String =
+        "A @Tail_Call annotation was placed in a non-tail-call position."
+    }
+
     /** Warnings about shadowing names. */
     sealed trait Shadowed extends Warning {
 
@@ -5343,6 +5430,24 @@ object IR {
           " importing the default definition from the Base.Vector module."
       }
 
+      /**
+        * An error coming from an unknown annotation name.
+        */
+      case object UnknownAnnotation extends Reason {
+        override def explain(originalName: Name): String =
+          s"The annotation ${originalName.name} is not defined."
+      }
+
+      /**
+        * An error coming from a tail call annotation placed in a syntactically
+        * incorrect position.
+        */
+      case object UnexpectedTailCallAnnotation extends Reason {
+        override def explain(originalName: Name): String =
+          s"Unexpected @TailCall annotation. This annotation can only be " +
+          s"used with function applications."
+      }
+
       /**
         * An error coming from an unexpected occurence of a polyglot symbol.
         *

engine/runtime/src/main/scala/org/enso/compiler/pass/analyse/DemandAnalysis.scala

@@ -166,6 +166,11 @@ case object DemandAnalysis extends IRPass {
           case lit: IR.Name.Literal => lit.copy(location = newNameLocation)
           case ths: IR.Name.This    => ths.copy(location = newNameLocation)
           case here: IR.Name.Here   => here.copy(location = newNameLocation)
+          case _: IR.Name.Annotation =>
+            throw new CompilerError(
+              "Annotations should not be present by the time demand analysis" +
+              " runs."
+            )
           case _: IR.Name.MethodReference =>
             throw new CompilerError(
               "Method references should not be present by the time demand " +

engine/runtime/src/main/scala/org/enso/compiler/pass/analyse/TailCall.scala

@@ -7,6 +7,7 @@ import org.enso.compiler.core.ir.MetadataStorage._
 import org.enso.compiler.exception.CompilerError
 import org.enso.compiler.pass.IRPass
 import org.enso.compiler.pass.desugar._
+import org.enso.compiler.pass.resolve.Annotations
 
 /** This pass performs tail call analysis on the Enso IR.
   *
@@ -128,14 +129,22 @@ case object TailCall extends IRPass {
     expression: IR.Expression,
     isInTailPosition: Boolean
   ): IR.Expression = {
-    expression match {
+    val expressionWithWarning =
+      if (
+        expression
+          .getMetadata(Annotations)
+          .contains(Annotations.TailCallAnnotated) && !isInTailPosition
+      ) expression.addDiagnostic(IR.Warning.WrongTco(expression.location))
+      else expression
+    expressionWithWarning match {
       case empty: IR.Empty =>
         empty.updateMetadata(this -->> TailPosition.NotTail)
-      case function: IR.Function => analyseFunction(function, isInTailPosition)
-      case caseExpr: IR.Case     => analyseCase(caseExpr, isInTailPosition)
-      case typ: IR.Type          => analyseType(typ, isInTailPosition)
-      case app: IR.Application   => analyseApplication(app, isInTailPosition)
-      case name: IR.Name         => analyseName(name, isInTailPosition)
+      case function: IR.Function =>
+        analyseFunction(function, isInTailPosition)
+      case caseExpr: IR.Case   => analyseCase(caseExpr, isInTailPosition)
+      case typ: IR.Type        => analyseType(typ, isInTailPosition)
+      case app: IR.Application => analyseApplication(app, isInTailPosition)
+      case name: IR.Name       => analyseName(name, isInTailPosition)
       case foreign: IR.Foreign =>
         foreign.updateMetadata(this -->> TailPosition.NotTail)
       case literal: IR.Literal => analyseLiteral(literal, isInTailPosition)
@@ -143,11 +152,19 @@ case object TailCall extends IRPass {
         throw new CompilerError(
           "Comments should not be present during tail call analysis."
         )
-      case block @ IR.Expression.Block(expressions, returnValue, _, _, _, _) =>
+      case block @ IR.Expression.Block(
+            expressions,
+            returnValue,
+            _,
+            _,
+            _,
+            _
+          ) =>
         block
           .copy(
-            expressions =
-              expressions.map(analyseExpression(_, isInTailPosition = false)),
+            expressions = expressions.map(
+              analyseExpression(_, isInTailPosition = false)
+            ),
             returnValue = analyseExpression(returnValue, isInTailPosition)
           )
           .updateMetadata(this -->> TailPosition.fromBool(isInTailPosition))
@@ -158,7 +175,9 @@ case object TailCall extends IRPass {
           )
           .updateMetadata(this -->> TailPosition.fromBool(isInTailPosition))
       case err: IR.Diagnostic =>
-        err.updateMetadata(this -->> TailPosition.fromBool(isInTailPosition))
+        err.updateMetadata(
+          this -->> TailPosition.fromBool(isInTailPosition)
+        )
     }
   }
 

engine/runtime/src/main/scala/org/enso/compiler/pass/optimise/LambdaConsolidate.scala

@@ -312,12 +312,13 @@ case object LambdaConsolidate extends IRPass {
               case defSpec: IR.DefinitionArgument.Specified => defSpec.name.name
             }
           )
-        case ths: IR.Name.This            => ths
-        case here: IR.Name.Here           => here
-        case blank: IR.Name.Blank         => blank
-        case ref: IR.Name.MethodReference => ref
-        case qual: IR.Name.Qualified      => qual
-        case err: IR.Error.Resolution     => err
+        case ths: IR.Name.This              => ths
+        case here: IR.Name.Here             => here
+        case blank: IR.Name.Blank           => blank
+        case ref: IR.Name.MethodReference   => ref
+        case qual: IR.Name.Qualified        => qual
+        case err: IR.Error.Resolution       => err
+        case annotation: IR.Name.Annotation => annotation
       }
     } else {
       name

engine/runtime/src/main/scala/org/enso/compiler/pass/resolve/Annotations.scala

@@ -0,0 +1,105 @@
+package org.enso.compiler.pass.resolve
+
+import org.enso.compiler.context.{InlineContext, ModuleContext}
+import org.enso.compiler.core.IR
+import org.enso.compiler.core.ir.MetadataStorage.ToPair
+import org.enso.compiler.exception.CompilerError
+import org.enso.compiler.pass.IRPass
+
+case object Annotations extends IRPass {
+  case object TailCallAnnotated extends IRPass.Metadata {
+    override val metadataName: String                 = "TailCallAnnotated"
+    override def duplicate(): Option[IRPass.Metadata] = Some(this)
+  }
+
+  val tailCallName = "@Tail_Call"
+
+  /** The type of the metadata object that the pass writes to the IR. */
+  override type Metadata = TailCallAnnotated.type
+
+  /** The type of configuration for the pass. */
+  override type Config = IRPass.Configuration.Default
+
+  /** The passes that this pass depends _directly_ on to run. */
+  override val precursorPasses: Seq[IRPass] = Seq()
+
+  /** The passes that are invalidated by running this pass. */
+  override val invalidatedPasses: Seq[IRPass] = Seq()
+
+  /** Executes the pass on the provided `ir`, and returns a possibly transformed
+    * or annotated version of `ir`.
+    *
+    * @param ir            the Enso IR to process
+    * @param moduleContext a context object that contains the information needed
+    *                      to process a module
+    * @return `ir`, possibly having made transformations or annotations to that
+    *         IR.
+    */
+  override def runModule(
+    ir: IR.Module,
+    moduleContext: ModuleContext
+  ): IR.Module = {
+    ir.mapExpressions(doExpression)
+  }
+
+  /** Executes the pass on the provided `ir`, and returns a possibly transformed
+    * or annotated version of `ir` in an inline context.
+    *
+    * @param ir            the Enso IR to process
+    * @param inlineContext a context object that contains the information needed
+    *                      for inline evaluation
+    * @return `ir`, possibly having made transformations or annotations to that
+    *         IR.
+    */
+  override def runExpression(
+    ir: IR.Expression,
+    inlineContext: InlineContext
+  ): IR.Expression = {
+    doExpression(ir)
+  }
+
+  private def doExpression(
+    ir: IR.Expression
+  ): IR.Expression =
+    ir.transformExpressions {
+      case app @ IR.Application.Prefix(
+            ann: IR.Name.Annotation,
+            arguments,
+            _,
+            _,
+            _,
+            _
+          ) =>
+        if (ann.name == tailCallName) {
+          arguments match {
+            case List() =>
+              throw new CompilerError(
+                "Impossible, application with no arguments."
+              )
+            case List(arg) =>
+              doExpression(arg.value)
+                .updateMetadata(this -->> TailCallAnnotated)
+            case realFun :: args =>
+              val recurFun  = doExpression(realFun.value)
+              val recurArgs = args.map(_.mapExpressions(doExpression))
+              app
+                .copy(function = recurFun, arguments = recurArgs)
+                .updateMetadata(this -->> TailCallAnnotated)
+          }
+        } else {
+          val err =
+            IR.Error.Resolution(ann, IR.Error.Resolution.UnknownAnnotation)
+          app.copy(function = err)
+        }
+      case ann: IR.Name.Annotation =>
+        if (ann.name == tailCallName) {
+          IR.Error.Resolution(
+            ann,
+            IR.Error.Resolution.UnexpectedTailCallAnnotation
+          )
+        } else {
+          IR.Error.Resolution(ann, IR.Error.Resolution.UnknownAnnotation)
+        }
+    }
+
+}

engine/runtime/src/test/scala/org/enso/compiler/test/PassesTest.scala

@@ -8,7 +8,15 @@ import org.enso.compiler.pass.analyse.{AliasAnalysis, BindingAnalysis}
 import org.enso.compiler.pass.desugar._
 import org.enso.compiler.pass.lint.ShadowedPatternFields
 import org.enso.compiler.pass.optimise.UnreachableMatchBranches
-import org.enso.compiler.pass.resolve.{DocumentationComments, IgnoredBindings, MethodDefinitions, ModuleThisToHere, TypeFunctions, TypeSignatures}
+import org.enso.compiler.pass.resolve.{
+  Annotations,
+  DocumentationComments,
+  IgnoredBindings,
+  MethodDefinitions,
+  ModuleThisToHere,
+  TypeFunctions,
+  TypeSignatures
+}
 
 class PassesTest extends CompilerTest {
 
@@ -56,7 +64,8 @@ class PassesTest extends CompilerTest {
           NestedPatternMatch,
           IgnoredBindings,
           TypeFunctions,
-          TypeSignatures
+          TypeSignatures,
+          Annotations
         )
       )
     }

engine/runtime/src/test/scala/org/enso/compiler/test/pass/analyse/TailCallTest.scala

@@ -149,9 +149,9 @@ class TailCallTest extends CompilerTest {
     val ir =
       """
         |a -> b -> c ->
-        |    d = a + b
+        |    d = @Tail_Call (a + b)
         |    e = a * c
-        |    d + e
+        |    @Tail_Call (d + e)
         |""".stripMargin.preprocessExpression.get.analyse
         .asInstanceOf[IR.Function.Lambda]
 
@@ -170,6 +170,22 @@ class TailCallTest extends CompilerTest {
         )
       )
     }
+
+    "warn about misplaced @TailCall annotations" in {
+      fnBody
+        .expressions(0)
+        .asInstanceOf[IR.Expression.Binding]
+        .expression
+        .diagnostics
+        .filter(_.isInstanceOf[IR.Warning.WrongTco])
+        .toList
+        .length shouldEqual 1
+
+      fnBody.returnValue.diagnostics
+        .filter(_.isInstanceOf[IR.Warning.WrongTco])
+        .toList
+        .length shouldEqual 0
+    }
   }
 
   "Tail call analysis on case expressions" should {

engine/runtime/src/test/scala/org/enso/compiler/test/pass/resolve/AnnotationsTest.scala

@@ -0,0 +1,100 @@
+package org.enso.compiler.test.pass.resolve
+
+import org.enso.compiler.Passes
+import org.enso.compiler.context.{FreshNameSupply, ModuleContext}
+import org.enso.compiler.core.IR
+import org.enso.compiler.pass.resolve.Annotations
+import org.enso.compiler.pass.{PassConfiguration, PassGroup, PassManager}
+import org.enso.compiler.test.CompilerTest
+
+class AnnotationsTest extends CompilerTest {
+
+  // === Test Setup ===========================================================
+
+  def mkModuleContext: ModuleContext =
+    buildModuleContext(
+      freshNameSupply = Some(new FreshNameSupply)
+    )
+
+  val passes = new Passes
+
+  val precursorPasses: PassGroup =
+    passes.getPrecursors(Annotations).get
+
+  val passConfiguration: PassConfiguration = PassConfiguration()
+
+  implicit val passManager: PassManager =
+    new PassManager(List(precursorPasses), passConfiguration)
+
+  /** Adds an extension method to analyse an Enso module.
+    *
+    * @param ir the ir to analyse
+    */
+  implicit class AnalyseModule(ir: IR.Module) {
+
+    /** Performs tail call analysis on [[ir]].
+      *
+      * @param context the module context in which analysis takes place
+      * @return [[ir]], with tail call analysis metadata attached
+      */
+    def analyse(implicit context: ModuleContext): IR.Module = {
+      Annotations.runModule(ir, context)
+    }
+  }
+
+  // === The Tests ============================================================
+
+  "Annotations resolution" should {
+    implicit val ctx: ModuleContext = mkModuleContext
+
+    val ir =
+      """
+        |foo x =
+        |    @Tail_Call
+        |    @Unknown_Annotation foo bar baz
+        |    foo @Tail_Call
+        |    foo (@Tail_Call bar baz)
+        |""".stripMargin.preprocessModule.analyse
+
+    "resolve and mark annotations" in {
+      val items = ir.bindings.head
+        .asInstanceOf[IR.Module.Scope.Definition.Method.Explicit]
+        .body
+        .asInstanceOf[IR.Function.Lambda]
+        .body
+        .asInstanceOf[IR.Expression.Block]
+      items.expressions(0) shouldBe an[IR.Error.Resolution]
+      items
+        .expressions(0)
+        .asInstanceOf[IR.Error.Resolution]
+        .reason shouldEqual IR.Error.Resolution.UnexpectedTailCallAnnotation
+
+      val unknown =
+        items.expressions(1).asInstanceOf[IR.Application.Prefix].function
+      unknown shouldBe an[IR.Error.Resolution]
+      unknown
+        .asInstanceOf[IR.Error.Resolution]
+        .reason shouldEqual IR.Error.Resolution.UnknownAnnotation
+
+      val misplaced = items
+        .expressions(2)
+        .asInstanceOf[IR.Application.Prefix]
+        .arguments(0)
+        .value
+      misplaced shouldBe an[IR.Error.Resolution]
+      misplaced
+        .asInstanceOf[IR.Error.Resolution]
+        .reason shouldEqual IR.Error.Resolution.UnexpectedTailCallAnnotation
+
+      val correct = items
+        .returnValue
+        .asInstanceOf[IR.Application.Prefix]
+        .arguments(0)
+        .value
+        .asInstanceOf[IR.Application.Prefix]
+      correct.function.asInstanceOf[IR.Name].name shouldEqual "bar"
+      correct.arguments.length shouldEqual 1
+      correct.getMetadata(Annotations) should contain(Annotations.TailCallAnnotated)
+    }
+  }
+}

engine/runtime/src/test/scala/org/enso/interpreter/test/instrument/RuntimeServerTest.scala

@@ -2756,6 +2756,11 @@ class RuntimeServerTest
                   Some(
                     model.Range(model.Position(2, 14), model.Position(2, 23))
                   )
+                ),
+                Api.StackTraceElement(
+                  "Main.main",
+                  Some(mainFile),
+                  Some(model.Range(model.Position(0, 7), model.Position(0, 19)))
                 )
               )
             )
@@ -2823,6 +2828,11 @@ class RuntimeServerTest
                   Some(
                     model.Range(model.Position(2, 10), model.Position(2, 15))
                   )
+                ),
+                Api.StackTraceElement(
+                  "Main.main",
+                  Some(mainFile),
+                  Some(model.Range(model.Position(0, 7), model.Position(0, 23)))
                 )
               )
             )
@@ -2976,6 +2986,11 @@ class RuntimeServerTest
                   "Main.foo",
                   Some(mainFile),
                   Some(model.Range(model.Position(5, 8), model.Position(5, 16)))
+                ),
+                Api.StackTraceElement(
+                  "Main.main",
+                  Some(mainFile),
+                  Some(model.Range(model.Position(2, 7), model.Position(2, 15)))
                 )
               )
             )

engine/runtime/src/test/scala/org/enso/interpreter/test/semantic/ExpressionIdTest.scala

@@ -74,12 +74,12 @@ class ExpressionIdTest extends InterpreterTest {
       val id1  = meta.addItem(106, 5)
       val id2  = meta.addItem(124, 1)
       val id3  = meta.addItem(120, 7)
-      val id4  = meta.addItem(133, 9)
+      val id4  = meta.addItem(132, 9)
 
       instrumenter.assertNodeExists(id1, "30")
       instrumenter.assertNodeExists(id2, "10")
-      instrumenter.assertNodeExistsTail(id3)
-      instrumenter.assertNodeExistsTail(id4)
+      instrumenter.assertNodeExists(id3, "30")
+      instrumenter.assertNodeExists(id4, "30")
       eval(meta.appendToCode(code))
     }
 

engine/runtime/src/test/scala/org/enso/interpreter/test/semantic/GroupingTest.scala

@@ -34,7 +34,7 @@ class GroupingTest extends InterpreterTest {
         """
           |main =
           |    ifTest = c -> (~ifT) -> ~ifF -> if c == 0 then ifT else ifF
-          |    sum = c -> acc -> ifTest c acc (sum c-1 acc+c)
+          |    sum = c -> acc -> ifTest c acc (@Tail_Call sum c-1 acc+c)
           |    sum 10000 0
           |""".stripMargin
 

engine/runtime/src/test/scala/org/enso/interpreter/test/semantic/RuntimeManagementTest.scala

@@ -25,7 +25,7 @@ class RuntimeManagementTest extends InterpreterTest {
           |
           |foo x =
           |    if x == 0 then IO.println "Start." else Unit
-          |    here.foo x+1
+          |    @Tail_Call here.foo x+1
           |
           |main =
           |    Thread.with_interrupt_handler (here.foo 0) (IO.println "Interrupted.")

engine/runtime/src/test/scala/org/enso/interpreter/test/semantic/SuspendedArgumentsTest.scala

@@ -38,7 +38,7 @@ class SuspendedArgumentsTest extends InterpreterTest {
         """
           |main =
           |    ifTest = c -> ~ifT -> ~ifF -> if c == 0 then ifT else ifF
-          |    sum = c -> acc -> ifTest c acc (sum c-1 acc+c)
+          |    sum = c -> acc -> ifTest c acc (@Tail_Call sum c-1 acc+c)
           |    sum 10000 0
           |""".stripMargin
       eval(code) shouldEqual 50005000

lib/scala/interpreter-dsl/src/main/java/org/enso/interpreter/dsl/BuiltinMethod.java

@@ -17,7 +17,4 @@ public @interface BuiltinMethod {
 
   /** @return a short description of this method. */
   String description();
-
-  /** @return whether it is safe to always call this function directly. */
-  boolean alwaysDirect() default true;
 }

lib/scala/interpreter-dsl/src/main/java/org/enso/interpreter/dsl/MethodProcessor.java

@@ -122,11 +122,6 @@ public class MethodProcessor extends AbstractProcessor {
       out.println("  public static Function makeFunction(Language language) {");
       out.println("    return Function." + functionBuilderMethod + "(");
       out.println("        new " + methodDefinition.getClassName() + "(language),");
-      if (methodDefinition.isAlwaysDirect()) {
-        out.println("        FunctionSchema.CallStrategy.ALWAYS_DIRECT,");
-      } else {
-        out.println("        FunctionSchema.CallStrategy.DIRECT_WHEN_TAIL,");
-      }
       List<String> argumentDefs = new ArrayList<>();
       for (MethodDefinition.ArgumentDefinition arg : methodDefinition.getArguments()) {
         if (arg.isPositional()) {

lib/scala/interpreter-dsl/src/main/java/org/enso/interpreter/dsl/model/MethodDefinition.java

@@ -172,11 +172,6 @@ public class MethodDefinition {
     return needsCallerInfo;
   }
 
-  /** @return whether this method can be always safely called directly. */
-  public boolean isAlwaysDirect() {
-    return annotation.alwaysDirect();
-  }
-
   public String getConstructorExpression() {
     return constructorExpression;
   }

lib/scala/syntax/definition/src/main/scala/org/enso/syntax/text/AST.scala

@@ -197,6 +197,7 @@ object Shape extends ShapeImplicit {
   final case class Opr[T](name: String) extends Ident[T] {
     val (prec, assoc) = opr.Info.of(name)
   }
+  final case class Annotation[T](name: String) extends Ident[T]
   final case class InvalidSuffix[T](elem: AST.Ident, suffix: String)
       extends Invalid[T]
       with Phantom
@@ -450,6 +451,13 @@ object Shape extends ShapeImplicit {
     implicit def ozip[T]: OffsetZip[Opr, T] = t => t.coerce
     implicit def span[T]: HasSpan[Opr[T]]   = t => t.name.length
   }
+  object Annotation {
+    implicit def ftor: Functor[Annotation]         = semi.functor
+    implicit def fold: Foldable[Annotation]        = semi.foldable
+    implicit def repr[T]: Repr[Annotation[T]]      = _.name
+    implicit def ozip[T]: OffsetZip[Annotation, T] = t => t.coerce
+    implicit def span[T]: HasSpan[Annotation[T]]   = t => t.name.length
+  }
   object InvalidSuffix {
     implicit def ftor: Functor[InvalidSuffix]         = semi.functor
     implicit def fold: Foldable[InvalidSuffix]        = semi.foldable
@@ -1140,6 +1148,7 @@ sealed trait ShapeImplicit {
     case s: Var[T]           => s.repr
     case s: Cons[T]          => s.repr
     case s: Opr[T]           => s.repr
+    case s: Annotation[T]    => s.repr
     case s: Mod[T]           => s.repr
     case s: InvalidSuffix[T] => s.repr
     case s: Number[T]        => s.repr
@@ -1182,6 +1191,7 @@ sealed trait ShapeImplicit {
     case s: Var[T]           => OffsetZip[Var, T].zipWithOffset(s)
     case s: Cons[T]          => OffsetZip[Cons, T].zipWithOffset(s)
     case s: Opr[T]           => OffsetZip[Opr, T].zipWithOffset(s)
+    case s: Annotation[T]    => OffsetZip[Annotation, T].zipWithOffset(s)
     case s: Mod[T]           => OffsetZip[Mod, T].zipWithOffset(s)
     case s: InvalidSuffix[T] => OffsetZip[InvalidSuffix, T].zipWithOffset(s)
     case s: Number[T]        => OffsetZip[Number, T].zipWithOffset(s)
@@ -1225,6 +1235,7 @@ sealed trait ShapeImplicit {
     case s: Var[T]           => s.span()
     case s: Cons[T]          => s.span()
     case s: Opr[T]           => s.span()
+    case s: Annotation[T]    => s.span()
     case s: Mod[T]           => s.span()
     case s: InvalidSuffix[T] => s.span()
     case s: Number[T]        => s.span()
@@ -1685,28 +1696,31 @@ object AST {
 
   //// Reexports ////
 
-  type Blank = Ident.Blank
-  type Var   = Ident.Var
-  type Cons  = Ident.Cons
-  type Opr   = Ident.Opr
-  type Mod   = Ident.Mod
+  type Blank      = Ident.Blank
+  type Var        = Ident.Var
+  type Cons       = Ident.Cons
+  type Opr        = Ident.Opr
+  type Mod        = Ident.Mod
+  type Annotation = Ident.Annotation
 
-  val Blank = Ident.Blank
-  val Var   = Ident.Var
-  val Cons  = Ident.Cons
-  val Opr   = Ident.Opr
-  val Mod   = Ident.Mod
+  val Blank      = Ident.Blank
+  val Var        = Ident.Var
+  val Cons       = Ident.Cons
+  val Opr        = Ident.Opr
+  val Mod        = Ident.Mod
+  val Annotation = Ident.Annotation
 
   //// Definition ////
 
   type Ident = ASTOf[Shape.Ident]
 
   object Ident {
-    type Blank = ASTOf[Shape.Blank]
-    type Var   = ASTOf[Shape.Var]
-    type Cons  = ASTOf[Shape.Cons]
-    type Mod   = ASTOf[Shape.Mod]
-    type Opr   = ASTOf[Shape.Opr]
+    type Blank      = ASTOf[Shape.Blank]
+    type Var        = ASTOf[Shape.Var]
+    type Cons       = ASTOf[Shape.Cons]
+    type Mod        = ASTOf[Shape.Mod]
+    type Opr        = ASTOf[Shape.Opr]
+    type Annotation = ASTOf[Shape.Annotation]
 
     type InvalidSuffix = ASTOf[Shape.InvalidSuffix]
 
@@ -1768,6 +1782,11 @@ object AST {
       def unapply(t: AST)          = Unapply[Opr].run(_.name)(t)
       def apply(name: String): Opr = Shape.Opr[AST](name)
     }
+    object Annotation {
+      val any                             = UnapplyByType[Annotation]
+      def unapply(t: AST)                 = Unapply[Annotation].run(_.name)(t)
+      def apply(name: String): Annotation = Shape.Annotation[AST](name)
+    }
   }
 
   //////////////////////////////////////////////////////////////////////////////

lib/scala/syntax/definition/src/main/scala/org/enso/syntax/text/ast/meta/Pattern.scala

@@ -64,17 +64,18 @@ object Pattern {
   final case class Cls     (cls  : Class , pat    : P)              extends P
 
   /** Token Patterns */
-  final case class Tok     (spaced : Spaced, ast  : AST)            extends P
-  final case class Blank   (spaced : Spaced)                        extends P
-  final case class Var     (spaced : Spaced)                        extends P
-  final case class Cons    (spaced : Spaced)                        extends P
-  final case class Opr     (spaced : Spaced, maxPrec: Option[Int])  extends P
-  final case class Mod     (spaced : Spaced)                        extends P
-  final case class Num     (spaced : Spaced)                        extends P
-  final case class Text    (spaced : Spaced)                        extends P
-  final case class Block   (spaced : Spaced)                        extends P
-  final case class Macro   (spaced : Spaced)                        extends P
-  final case class Invalid (spaced : Spaced)                        extends P
+  final case class Tok       (spaced : Spaced, ast  : AST)            extends P
+  final case class Blank     (spaced : Spaced)                        extends P
+  final case class Var       (spaced : Spaced)                        extends P
+  final case class Cons      (spaced : Spaced)                        extends P
+  final case class Opr       (spaced : Spaced, maxPrec: Option[Int])  extends P
+  final case class Annotation(spaced : Spaced)                        extends P
+  final case class Mod       (spaced : Spaced)                        extends P
+  final case class Num       (spaced : Spaced)                        extends P
+  final case class Text      (spaced : Spaced)                        extends P
+  final case class Block     (spaced : Spaced)                        extends P
+  final case class Macro     (spaced : Spaced)                        extends P
+  final case class Invalid   (spaced : Spaced)                        extends P
   // format: on
 
   //// Smart Constructors ////
@@ -95,6 +96,10 @@ object Pattern {
     def apply(spaced: Spaced): Opr  = Opr(spaced, None)
     def apply(spaced: Boolean): Opr = Opr(Some(spaced))
   }
+  object Annotation {
+    def apply(): Annotation                = Annotation(None)
+    def apply(spaced: Boolean): Annotation = Annotation(Some(spaced))
+  }
   object Num {
     def apply(): Num                = Num(None)
     def apply(spaced: Boolean): Num = Num(Some(spaced))
@@ -113,6 +118,7 @@ object Pattern {
     Var(spaced) |
     Cons(spaced) |
     Opr(spaced) |
+    Annotation(spaced) |
     Mod(spaced) |
     Num(spaced) |
     Text(spaced) |
@@ -183,17 +189,18 @@ object Pattern {
     final case class Cls   [T](pat:P.Cls   , elem:M[T])             extends M[T]
 
     /** Token Matches */
-    final case class Tok     [T](pat:P.Tok     , elem:T)            extends M[T]
-    final case class Blank   [T](pat:P.Blank   , elem:T)            extends M[T]
-    final case class Var     [T](pat:P.Var     , elem:T)            extends M[T]
-    final case class Cons    [T](pat:P.Cons    , elem:T)            extends M[T]
-    final case class Opr     [T](pat:P.Opr     , elem:T)            extends M[T]
-    final case class Mod     [T](pat:P.Mod     , elem:T)            extends M[T]
-    final case class Num     [T](pat:P.Num     , elem:T)            extends M[T]
-    final case class Text    [T](pat:P.Text    , elem:T)            extends M[T]
-    final case class Block   [T](pat:P.Block   , elem:T)            extends M[T]
-    final case class Macro   [T](pat:P.Macro   , elem:T)            extends M[T]
-    final case class Invalid [T](pat:P.Invalid , elem:T)            extends M[T]
+    final case class Tok       [T](pat:P.Tok        , elem:T) extends M[T]
+    final case class Blank     [T](pat:P.Blank      , elem:T) extends M[T]
+    final case class Var       [T](pat:P.Var        , elem:T) extends M[T]
+    final case class Cons      [T](pat:P.Cons       , elem:T) extends M[T]
+    final case class Opr       [T](pat:P.Opr        , elem:T) extends M[T]
+    final case class Annotation[T](pat:P.Annotation , elem:T) extends M[T]
+    final case class Mod       [T](pat:P.Mod        , elem:T) extends M[T]
+    final case class Num       [T](pat:P.Num        , elem:T) extends M[T]
+    final case class Text      [T](pat:P.Text       , elem:T) extends M[T]
+    final case class Block     [T](pat:P.Block      , elem:T) extends M[T]
+    final case class Macro     [T](pat:P.Macro      , elem:T) extends M[T]
+    final case class Invalid   [T](pat:P.Invalid    , elem:T) extends M[T]
     // format: on
 
     //// Smart Constructors ////
@@ -228,28 +235,29 @@ object Pattern {
     @nowarn("cat=unchecked")
     def mapStructShallow(f: MatchOf[T] => MatchOf[T]): MatchOf[T] =
       this match {
-        case m: M.Begin[T]   => m
-        case m: M.End[T]     => m
-        case m: M.Nothing[T] => m
-        case m: M.Seq[T]     => m.copy(elem = m.elem.bimap(f, f))
-        case m: M.Or[T]      => m.copy(elem = m.elem.bimap(f, f))
-        case m: M.Many[T]    => m.copy(elem = m.elem.map(f))
-        case m: M.Except[T]  => m.copy(elem = f(m.elem))
-        case m: M.Build[T]   => m
-        case m: M.Err[T]     => m
-        case m: M.Tag[T]     => m.copy(elem = f(m.elem))
-        case m: M.Cls[T]     => m.copy(elem = f(m.elem))
-        case m: M.Tok[T]     => m
-        case m: M.Blank[T]   => m
-        case m: M.Var[T]     => m
-        case m: M.Cons[T]    => m
-        case m: M.Opr[T]     => m
-        case m: M.Mod[T]     => m
-        case m: M.Num[T]     => m
-        case m: M.Text[T]    => m
-        case m: M.Block[T]   => m
-        case m: M.Macro[T]   => m
-        case m: M.Invalid[T] => m
+        case m: M.Begin[T]      => m
+        case m: M.End[T]        => m
+        case m: M.Nothing[T]    => m
+        case m: M.Seq[T]        => m.copy(elem = m.elem.bimap(f, f))
+        case m: M.Or[T]         => m.copy(elem = m.elem.bimap(f, f))
+        case m: M.Many[T]       => m.copy(elem = m.elem.map(f))
+        case m: M.Except[T]     => m.copy(elem = f(m.elem))
+        case m: M.Build[T]      => m
+        case m: M.Err[T]        => m
+        case m: M.Tag[T]        => m.copy(elem = f(m.elem))
+        case m: M.Cls[T]        => m.copy(elem = f(m.elem))
+        case m: M.Tok[T]        => m
+        case m: M.Blank[T]      => m
+        case m: M.Var[T]        => m
+        case m: M.Cons[T]       => m
+        case m: M.Opr[T]        => m
+        case m: M.Annotation[T] => m
+        case m: M.Mod[T]        => m
+        case m: M.Num[T]        => m
+        case m: M.Text[T]       => m
+        case m: M.Block[T]      => m
+        case m: M.Macro[T]      => m
+        case m: M.Invalid[T]    => m
       }
 
     @nowarn("cat=unchecked")
@@ -304,6 +312,8 @@ object Pattern {
         case m: M.Cons[T] =>
           (m.copy(elem = f(off, m.elem)), off + m.elem.span())
         case m: M.Opr[T] => (m.copy(elem = f(off, m.elem)), off + m.elem.span())
+        case m: M.Annotation[T] =>
+          (m.copy(elem = f(off, m.elem)), off + m.elem.span())
         case m: M.Mod[T] => (m.copy(elem = f(off, m.elem)), off + m.elem.span())
         case m: M.Num[T] => (m.copy(elem = f(off, m.elem)), off + m.elem.span())
         case m: M.Text[T] =>
@@ -534,6 +544,8 @@ sealed trait Pattern {
           matchByCls[AST.Opr](spaced) { sast =>
             Option.when(maxPrec.forall(_ >= sast.wrapped.prec))(M.Opr(p, sast))
           }
+        case p @ P.Annotation(spaced) =>
+          matchByCls_[AST.Annotation](spaced, M.Annotation(p, _))
         case p @ P.Mod(spaced) => matchByCls_[AST.Mod](spaced, M.Mod(p, _))
 
         case p @ P.Macro(spaced) =>

lib/scala/syntax/definition/src/main/scala/org/enso/syntax/text/spec/ParserDef.scala

@@ -180,21 +180,23 @@ case class ParserDef() extends flexer.Parser[AST.Module] {
         if (current.isDefined) submit()
       }
 
-    val char: Pattern   = alphaNum | '_'
-    val body: Pattern   = char.many >> '\''.many
-    val _var: Pattern   = lowerLetter >> body
-    val cons: Pattern   = upperLetter >> body
-    val breaker: String = "^`!@#$%^&*()-=+[]{}|;:<>,./ \t\r\n\\"
-    val errSfx: Pattern = noneOf(breaker).many1
+    val char: Pattern       = alphaNum | '_'
+    val body: Pattern       = char.many >> '\''.many
+    val _var: Pattern       = lowerLetter >> body
+    val cons: Pattern       = upperLetter >> body
+    val annotation: Pattern = "@" >> cons
+    val breaker: String     = "^`!@#$%^&*()-=+[]{}|;:<>,./ \t\r\n\\"
+    val errSfx: Pattern     = noneOf(breaker).many1
 
     val SFX_CHECK = state.define("Identifier Suffix Check")
   }
 
-  ROOT            || ident._var   || ident.on(AST.Var(_))
-  ROOT            || ident.cons   || ident.on(AST.Cons(_))
-  ROOT            || "_"          || ident.on(AST.Blank())
-  ident.SFX_CHECK || ident.errSfx || ident.onErrSfx()
-  ident.SFX_CHECK || always       || ident.onNoErrSfx()
+  ROOT            || ident._var       || ident.on(AST.Var(_))
+  ROOT            || ident.cons       || ident.on(AST.Cons(_))
+  ROOT            || "_"              || ident.on(AST.Blank())
+  ROOT            || ident.annotation || ident.on(AST.Annotation(_))
+  ident.SFX_CHECK || ident.errSfx     || ident.onErrSfx()
+  ident.SFX_CHECK || always           || ident.onNoErrSfx()
 
   //////////////////
   //// Operator ////

lib/scala/syntax/specialization/shared/src/test/scala/org/enso/syntax/text/ParserTest.scala

@@ -77,16 +77,17 @@ class ParserTest extends AnyFlatSpec with Matchers {
   //// Identifiers /////////////////////////////////////////////////////////////
   //////////////////////////////////////////////////////////////////////////////
 
-  "_"      ?= "_"
-  "Name"   ?= "Name"
-  "name"   ?= "name"
-  "name'"  ?= "name'"
-  "name''" ?= "name''"
-  "name'a" ?= Ident.InvalidSuffix("name'", "a")
-  "name_"  ?= "name_"
-  "name_'" ?= "name_'"
-  "name'_" ?= Ident.InvalidSuffix("name'", "_")
-  "name`"  ?= "name" $ Invalid.Unrecognized("`")
+  "_"           ?= "_"
+  "Name"        ?= "Name"
+  "name"        ?= "name"
+  "name'"       ?= "name'"
+  "name''"      ?= "name''"
+  "name'a"      ?= Ident.InvalidSuffix("name'", "a")
+  "name_"       ?= "name_"
+  "name_'"      ?= "name_'"
+  "name'_"      ?= Ident.InvalidSuffix("name'", "_")
+  "name`"       ?= "name" $ Invalid.Unrecognized("`")
+  "@Annotation" ?= Ident.Annotation("@Annotation")
 
   //////////////////////////////////////////////////////////////////////////////
   //// Operators ///////////////////////////////////////////////////////////////

test/Benchmarks/src/Collections.enso

@@ -4,21 +4,13 @@ import Base.Bench_Utils
 
 gen_list len = 0.upto len . fold Nil (l -> i -> Cons i+1 l)
 
-sum_vec vec =
-    arr = vec.to_array
-    len = vec.length
-    sumator = acc -> idx ->
-        if idx == len then acc else sumator (acc + arr.at idx) idx+1
-    res = sumator 0 0
-    res
-
 sum_list_meta list =
     nil_cons = Meta.meta Nil . constructor
     folder acc list =
         meta_list = Meta.meta list
         if meta_list.constructor == nil_cons then acc else
             fs = meta_list.fields
-            folder (acc + fs.at 0) (fs.at 1)
+            @Tail_Call folder (acc + fs.at 0) (fs.at 1)
     res = folder 0 list
     res
 

test/Benchmarks/src/Main.enso

@@ -8,27 +8,31 @@ type Sum
 
 sum_tco = sum_to ->
     summator = acc -> current ->
-        if current == 0 then acc else summator acc+current current-1
+        if current == 0 then acc else
+            @Tail_Call summator acc+current current-1
     res = summator 0 sum_to
     res
 
 sum_tco_decimal = sum_to ->
     s = sum_to.to_decimal
     summator = acc -> current ->
-        if current >= s then acc else summator acc+current current+1.0
+        if current >= s then acc else
+            @Tail_Call summator acc+current current+1.0
     res = summator 0.0 0.0
     res
 
 sum_tco_eval = sumTo ->
     summator = acc -> current ->
-        if current == 0 then acc else Debug.eval "summator (acc + current) (current - 1)"
+        if current == 0 then acc else
+            Debug.eval "@Tail_Call summator (acc + current) (current - 1)"
 
     res = summator 0 sumTo
     res
 
 sum_tco_java = sum_to ->
     summator = acc -> current ->
-        if current == 0 then acc else summator (Long.sum [acc, current]) (current - 1)
+        if current == 0 then acc else
+            @Tail_Call summator (Long.sum [acc, current]) (current - 1)
     res = summator 0 sum_to
     res
 
@@ -37,7 +41,7 @@ sum_co_state_body =
     acc = State.get Sum
     State.put Counter n-1
     State.put Sum     acc+n
-    if n == 0 then acc else here.sum_co_state_body
+    if n == 0 then acc else @Tail_Call here.sum_co_state_body
 
 sum_co_state n =
     res = State.run Counter n (State.run Sum 0 here.sum_co_state_body)
@@ -46,14 +50,26 @@ sum_co_state n =
 sum_state_body n =
     acc = State.get Number
     State.put Number (acc + n)
-    if n == 0 then State.get Number else here.sum_state_body (n - 1)
+    if n == 0 then State.get Number else
+        @Tail_Call here.sum_state_body (n - 1)
 
 sum_state = sum_to ->
     res = State.run Number 0 (here.sum_state_body sum_to)
     res
 
+sum_co_1 n acc = if n == 0 then acc else @Tail_Call here.sum_co_2 n-1 acc+n
+
+sum_co_2 n acc = if n == 0 then acc else here.sum_co_1 n-1 acc+n
+
+sum_co n =
+    res = here.sum_co_2 n 0
+    res
+
 main =
     hundred_mil = 100000000
+    IO.println (here.sum_co 1000)
+    IO.println "Measuring Sum TCO Corecursive"
+    Bench_Utils.measure (here.sum_co hundred_mil) "sum_tco_corecursive" 100 10
     IO.println "Measuring Sum TCO Decimal"
     Bench_Utils.measure (here.sum_tco_decimal hundred_mil) "sum_tco_float" 100 10
     IO.println "Measuring SumTCO"

tools/performance/comparative-benchmark/benchmarks/haskell/package.yaml

@@ -15,6 +15,7 @@ library:
   dependencies:
     - base
     - deepseq
+    - containers
 
 benchmarks:
   haskell-benchmark:

tools/performance/comparative-benchmark/benchmarks/haskell/src/Fixtures.hs

@@ -2,8 +2,10 @@ module Fixtures where
 
 import Prelude
 
-import Data.Int (Int64)
+import qualified Data.Map.Strict as Map
 
+import Data.Int (Int64)
+import Data.List (foldl')
 
 
 ------------------
@@ -12,8 +14,6 @@ import Data.Int (Int64)
 
 data List a = Cons a (List a) | Nil deriving (Show)
 
-
-
 --------------------------
 -- === Input Values === --
 --------------------------
@@ -32,7 +32,8 @@ millionElementList = genList 1000000
 hundredMillion :: Int64
 hundredMillion = 100000000
 
-
+tenThousand :: Integer
+tenThousand = 10000
 
 ----------------------
 -- === Fixtures === --
@@ -67,3 +68,5 @@ myFoldl _ z Nil         = z
 myFoldl f z (Cons x xs) = let z' = z `f` x
                     in seq z' $ myFoldl f z' xs
 
+buildMap :: Integer -> Map.Map Integer Integer
+buildMap i = foldl' (\m i -> Map.insert i i m) Map.empty [0..i]

tools/performance/comparative-benchmark/benchmarks/haskell/test/bench/Main.hs

@@ -9,6 +9,7 @@ import Criterion.Main
 main :: IO ()
 main = defaultMain
     [
+        bench "buildMap"        $ whnf Fixtures.buildMap Fixtures.tenThousand,
         bench "sumTCO"          $ whnf Fixtures.sumTCO Fixtures.hundredMillion,
         bench "sumList"         $ whnf Fixtures.sumList Fixtures.millionElementList,
         bench "reverseList"     $ whnf Fixtures.reverseList Fixtures.millionElementList,