From 9d1f545ad6722ecc2f7453e8cf5afd6f80db1f13 Mon Sep 17 00:00:00 2001
From: Folkert <folkert@folkertdev.nl>
Date: Fri, 7 Aug 2020 00:45:12 +0200
Subject: [PATCH] implement free variables

---
 compiler/mono/src/inc_dec.rs | 123 +++++++++++++++++++++++++++++++++++
 compiler/mono/src/lib.rs     |   1 +
 2 files changed, 124 insertions(+)
 create mode 100644 compiler/mono/src/inc_dec.rs

diff --git a/compiler/mono/src/inc_dec.rs b/compiler/mono/src/inc_dec.rs
new file mode 100644
index 0000000000..e8ba7ed404
--- /dev/null
+++ b/compiler/mono/src/inc_dec.rs
@@ -0,0 +1,123 @@
+use crate::ir::{Expr, Stmt};
+use roc_collections::all::MutSet;
+use roc_module::symbol::Symbol;
+
+pub fn free_variables(stmt: &Stmt<'_>) -> MutSet<Symbol> {
+    let (mut occuring, bound) = occuring_variables(stmt);
+
+    for ref s in bound {
+        occuring.remove(s);
+    }
+
+    occuring
+}
+
+pub fn occuring_variables(stmt: &Stmt<'_>) -> (MutSet<Symbol>, MutSet<Symbol>) {
+    let mut stack = vec![stmt];
+    let mut result = MutSet::default();
+    let mut bound_variables = MutSet::default();
+
+    while let Some(stmt) = stack.pop() {
+        use Stmt::*;
+
+        match stmt {
+            Let(symbol, expr, _, cont) => {
+                occuring_variables_expr(expr, &mut result);
+                result.insert(*symbol);
+                bound_variables.insert(*symbol);
+                stack.push(cont);
+            }
+            Ret(symbol) => {
+                result.insert(*symbol);
+            }
+
+            Inc(symbol, cont) | Dec(symbol, cont) => {
+                result.insert(*symbol);
+                stack.push(cont);
+            }
+
+            Jump(_, arguments) => {
+                result.extend(arguments.iter().copied());
+            }
+
+            Join {
+                arguments,
+                continuation,
+                remainder,
+                ..
+            } => {
+                result.extend(arguments.iter().map(|(s, _)| s).copied());
+
+                stack.push(continuation);
+                stack.push(remainder);
+            }
+
+            Switch {
+                cond_symbol,
+                branches,
+                default_branch,
+                ..
+            } => {
+                result.insert(*cond_symbol);
+
+                stack.extend(branches.iter().map(|(_, s)| s));
+                stack.push(default_branch);
+            }
+
+            Cond {
+                cond_symbol,
+                branching_symbol,
+                pass,
+                fail,
+                ..
+            } => {
+                result.insert(*cond_symbol);
+                result.insert(*branching_symbol);
+
+                stack.push(pass);
+                stack.push(fail);
+            }
+
+            RuntimeError(_) => {}
+        }
+    }
+
+    (result, bound_variables)
+}
+
+pub fn occuring_variables_expr(expr: &Expr<'_>, result: &mut MutSet<Symbol>) {
+    use crate::ir::CallType;
+    use Expr::*;
+
+    match expr {
+        FunctionPointer(symbol, _)
+        | Alias(symbol)
+        | AccessAtIndex {
+            structure: symbol, ..
+        } => {
+            result.insert(*symbol);
+        }
+
+        FunctionCall {
+            call_type, args, ..
+        } => {
+            result.extend(args.iter().copied());
+
+            match call_type {
+                CallType::ByName(s) => result.insert(*s),
+                CallType::ByPointer(s) => result.insert(*s),
+            };
+        }
+
+        RunLowLevel(_, arguments)
+        | Tag { arguments, .. }
+        | Struct(arguments)
+        | Array {
+            elems: arguments, ..
+        } => {
+            result.extend(arguments.iter().copied());
+        }
+
+        EmptyArray | RuntimeErrorFunction(_) | Literal(_) => {}
+    }
+}
diff --git a/compiler/mono/src/lib.rs b/compiler/mono/src/lib.rs
index 88d57302d6..22abce575d 100644
--- a/compiler/mono/src/lib.rs
+++ b/compiler/mono/src/lib.rs
@@ -11,6 +11,7 @@
 // re-enable this when working on performance optimizations than have it block PRs.
 #![allow(clippy::large_enum_variant)]
 
+pub mod inc_dec;
 pub mod ir;
 pub mod layout;