merge main

crates/compiler/builtins/roc/List.roc

@@ -73,6 +73,8 @@ module [
     countIf,
     chunksOf,
     concatUtf8,
+    forEach!,
+    forEachTry!,
 ]
 
 import Bool exposing [Bool, Eq]
@@ -1432,3 +1434,45 @@ iterBackwardsHelp = \list, state, f, prevIndex ->
 concatUtf8 : List U8, Str -> List U8
 
 expect (List.concatUtf8 [1, 2, 3, 4] "🐦") == [1, 2, 3, 4, 240, 159, 144, 166]
+
+## Run an effectful function for each element on the list.
+##
+## ```roc
+## List.forEach! ["Alice", "Bob", "Charlie"] \name ->
+##     createAccount! name
+##     log! "Account created"
+## ```
+##
+## If the function might fail or you need to return early, use [forEachTry!].
+forEach! : List a, (a => {}) => {}
+forEach! = \list, func! ->
+    when list is
+        [] ->
+            {}
+
+        [elem, .. as rest] ->
+            func! elem
+            forEach! rest func!
+
+## Run an effectful function that might fail for each element on the list.
+##
+## If the function returns `Err`, the iteration stops and the error is returned.
+##
+## ```roc
+## List.forEachTry! filesToDelete \path ->
+##     try File.delete! path
+##     Stdout.line! "$(path) deleted"
+## ```
+forEachTry! : List a, (a => Result {} err) => Result {} err
+forEachTry! = \list, func! ->
+    when list is
+        [] ->
+            Ok {}
+
+        [elem, .. as rest] ->
+            when func! elem is
+                Ok {} ->
+                    forEachTry! rest func!
+
+                Err err ->
+                    Err err

crates/compiler/builtins/roc/Result.roc

@@ -8,6 +8,7 @@ module [
     map2,
     try,
     onErr,
+    onErr!,
     withDefault,
 ]
 
@@ -119,3 +120,16 @@ onErr = \result, transform ->
     when result is
         Ok v -> Ok v
         Err e -> transform e
+
+## Like [onErr], but it allows the transformation function to produce effects.
+##
+## ```roc
+## Result.onErr (Err "missing user") \msg ->
+##     try Stdout.line! "ERROR: $(msg)"
+##     Err msg
+## ```
+onErr! : Result a err, (err => Result a otherErr) => Result a otherErr
+onErr! = \result, transform! ->
+    when result is
+        Ok v -> Ok v
+        Err e -> transform! e