add walkUntil and use it to implement set equality

crates/compiler/builtins/roc/Dict.roc

@@ -13,6 +13,7 @@ interface Dict
         remove,
         update,
         walk,
+        walkUntil,
         toList,
         fromList,
         keys,
@@ -190,6 +191,21 @@ walk : Dict k v, state, (state, k, v -> state) -> state | k has Hash & Eq
 walk = \@Dict { data }, initialState, transform ->
     List.walk data initialState (\state, T k v -> transform state k v)
 
+## Same as [Dict.walk], except you can stop walking early.
+##
+## ## Performance Details
+##
+## Compared to [Dict.walk], this can potentially visit fewer elements (which can
+## improve performance) at the cost of making each step take longer.
+## However, the added cost to each step is extremely small, and can easily
+## be outweighed if it results in skipping even a small number of elements.
+##
+## As such, it is typically better for performance to use this over [Dict.walk]
+## if returning `Break` earlier than the last element is expected to be common.
+walkUntil : Dict k v, state, (state, k, v -> [Continue state, Break state]) -> state | k has Hash & Eq
+walkUntil = \@Dict { data }, initialState, transform ->
+    List.walkUntil data initialState (\state, T k v -> transform state k v)
+
 ## Get the value for a given key. If there is a value for the specified key it
 ## will return [Ok value], otherwise return [Err KeyNotFound].
 ##

crates/compiler/builtins/roc/Set.roc

@@ -33,7 +33,15 @@ Set k := Dict.Dict k {}
      ]
 
 isEq : Set k, Set k -> Bool | k has Hash & Eq
-isEq = \_, _ -> Bool.true
+isEq = \xs, ys ->
+    if len xs != len ys then
+        Bool.false
+    else
+        walkUntil xs Bool.true \_, elem ->
+            if contains ys elem then
+                Continue Bool.true
+            else
+                Break Bool.false
 
 ## An empty set.
 empty : Set k | k has Hash & Eq
@@ -114,3 +122,57 @@ difference = \@Set dict1, @Set dict2 ->
 walk : Set k, state, (state, k -> state) -> state | k has Hash & Eq
 walk = \@Set dict, state, step ->
     Dict.walk dict state (\s, k, _ -> step s k)
+
+walkUntil : Set k, state, (state, k -> [Continue state, Break state]) -> state | k has Hash & Eq
+walkUntil = \@Set dict, state, step ->
+    Dict.walkUntil dict state (\s, k, _ -> step s k)
+
+expect
+    first =
+        single "Keep Me"
+        |> insert "And Me"
+        |> insert "Remove Me"
+
+    second =
+        single "Remove Me"
+        |> insert "I do nothing..."
+
+    expected =
+        single "Keep Me"
+        |> insert "And Me"
+
+    difference first second == expected
+
+expect
+    first =
+        single "Keep Me"
+        |> insert "And Me"
+        |> insert "Remove Me"
+
+    second =
+        single "Remove Me"
+        |> insert "I do nothing..."
+
+    expected =
+        single "Keep Me"
+        |> insert "And Me"
+
+    difference first second == expected
+
+expect
+    first =
+        single 1
+        |> insert 2
+
+    second =
+        single 1
+        |> insert 3
+        |> insert 4
+
+    expected =
+        single 1
+        |> insert 2
+        |> insert 3
+        |> insert 4
+
+    union first second == expected

crates/compiler/module/src/symbol.rs

@@ -1409,20 +1409,21 @@ define_builtins! {
         9 DICT_REMOVE: "remove"
 
         10 DICT_WALK: "walk"
-        11 DICT_FROM_LIST: "fromList"
-        12 DICT_TO_LIST: "toList"
-        13 DICT_KEYS: "keys"
-        14 DICT_VALUES: "values"
+        11 DICT_WALK_UNTIL: "walkUntil"
+        12 DICT_FROM_LIST: "fromList"
+        13 DICT_TO_LIST: "toList"
+        14 DICT_KEYS: "keys"
+        15 DICT_VALUES: "values"
 
-        15 DICT_INSERT_ALL: "insertAll" // union
-        16 DICT_KEEP_SHARED: "keepShared" // intersection
-        17 DICT_REMOVE_ALL: "removeAll" // difference
+        16 DICT_INSERT_ALL: "insertAll" // union
+        17 DICT_KEEP_SHARED: "keepShared" // intersection
+        18 DICT_REMOVE_ALL: "removeAll" // difference
 
-        18 DICT_WITH_CAPACITY: "withCapacity"
-        19 DICT_CAPACITY: "capacity"
-        20 DICT_UPDATE: "update"
+        19 DICT_WITH_CAPACITY: "withCapacity"
+        20 DICT_CAPACITY: "capacity"
+        21 DICT_UPDATE: "update"
 
-        21 DICT_LIST_GET_UNSAFE: "listGetUnsafe"
+        22 DICT_LIST_GET_UNSAFE: "listGetUnsafe"
     }
     9 SET: "Set" => {
         0 SET_SET: "Set" exposed_type=true // the Set.Set type alias
@@ -1437,10 +1438,11 @@ define_builtins! {
         9 SET_TO_LIST: "toList"
         10 SET_FROM_LIST: "fromList"
         11 SET_WALK: "walk"
-        12 SET_WALK_USER_FUNCTION: "#walk_user_function"
-        13 SET_CONTAINS: "contains"
-        14 SET_TO_DICT: "toDict"
-        15 SET_CAPACITY: "capacity"
+        12 SET_WALK_UNTIL: "walkUntil"
+        13 SET_WALK_USER_FUNCTION: "#walk_user_function"
+        14 SET_CONTAINS: "contains"
+        15 SET_TO_DICT: "toDict"
+        16 SET_CAPACITY: "capacity"
     }
     10 BOX: "Box" => {
         0 BOX_BOX_TYPE: "Box" exposed_apply_type=true // the Box.Box opaque type