fix: Fix Foldable1 NonEmptyArray instance (requires purescript/purescript-nonempty#39)

Author: srghma

src/Data/Array/NonEmpty/Internal.js

@@ -1,6 +1,6 @@
 "use strict";
 
-exports.fold1Impl = function (f) {
+exports.foldr1Impl = function (f) {
   return function (xs) {
     var acc = xs[0];
     var len = xs.length;
@@ -11,6 +11,16 @@ exports.fold1Impl = function (f) {
   };
 };
 
+exports.foldl1Impl = function (f) {
+  return function (xs) {
+    var acc = xs[xs.length - 1];
+    for (var i = xs.length - 2; i >= 0; i--) {
+      acc = f(xs[i])(acc);
+    }
+    return acc;
+  };
+};
+
 exports.traverse1Impl = function () {
   function Cont(fn) {
     this.fn = fn;

src/Data/Array/NonEmpty/Internal.purs

@@ -35,7 +35,9 @@ derive newtype instance foldableWithIndexNonEmptyArray :: FoldableWithIndex Int
 
 instance foldable1NonEmptyArray :: Foldable1 NonEmptyArray where
   foldMap1 = foldMap1Default
-  fold1 = fold1Impl (<>)
+  fold1 = foldr1Impl (<>)
+  foldr1 = foldr1Impl
+  foldl1 = foldl1Impl
 
 derive newtype instance unfoldable1NonEmptyArray :: Unfoldable1 NonEmptyArray
 derive newtype instance traversableNonEmptyArray :: Traversable NonEmptyArray
@@ -56,7 +58,8 @@ derive newtype instance monadNonEmptyArray :: Monad NonEmptyArray
 derive newtype instance altNonEmptyArray :: Alt NonEmptyArray
 
 -- we use FFI here to avoid the unncessary copy created by `tail`
-foreign import fold1Impl :: forall a. (a -> a -> a) -> NonEmptyArray a -> a
+foreign import foldr1Impl :: forall a. (a -> a -> a) -> NonEmptyArray a -> a
+foreign import foldl1Impl :: forall a. (a -> a -> a) -> NonEmptyArray a -> a
 
 foreign import traverse1Impl
   :: forall m a b

test/Test/Data/Array/NonEmpty.purs

@@ -10,7 +10,7 @@ import Data.FunctorWithIndex (mapWithIndex)
 import Data.Maybe (Maybe(..), fromJust)
 import Data.Monoid.Additive (Additive(..))
 import Data.NonEmpty ((:|))
-import Data.Semigroup.Foldable (foldMap1)
+import Data.Semigroup.Foldable (foldMap1, foldr1, foldl1)
 import Data.Semigroup.Traversable (traverse1)
 import Data.Tuple (Tuple(..))
 import Data.Unfoldable1 as U1
@@ -297,12 +297,22 @@ testNonEmptyArray = do
   log "Unfoldable instance"
   assert $ U1.range 0 9 == NEA.range 0 9
 
-  log "foldl should work"
+  log "foldMap1 should work"
+  assert $ foldMap1 Additive (fromArray [1, 2, 3, 4]) == Additive 10
+
+  log "fold1 should work"
   -- test through sum
   assert $ sum (fromArray [1, 2, 3, 4]) == 10
 
-  log "foldMap1 should work"
-  assert $ foldMap1 Additive (fromArray [1, 2, 3, 4]) == Additive 10
+  log "foldr1 should work"
+  assert $ foldr1 (\l r -> "(" <> l <> r <> ")") (fromArray ["a", "b", "c", "d"]) == "(((ab)c)d)"
+  assert $ foldr1 (\l r -> "(" <> l <> r <> ")") (fromArray ["a", "b"])           == "(ab)"
+  assert $ foldr1 (\l r -> "(" <> l <> r <> ")") (fromArray ["a"])                == "a"
+
+  log "foldl1 should work"
+  assert $ foldl1 (\l r -> "(" <> l <> r <> ")") (fromArray ["a", "b", "c", "d"]) == "(a(b(cd)))"
+  assert $ foldl1 (\l r -> "(" <> l <> r <> ")") (fromArray ["a", "b"])           == "(ab)"
+  assert $ foldl1 (\l r -> "(" <> l <> r <> ")") (fromArray ["a"])                == "a"
 
   log "traverse1 should work"
   assert $ traverse1 Just (fromArray [1, 2, 3, 4]) == NEA.fromArray [1, 2, 3, 4]