From 64be83764566a35653ad00bbdf1266a0b327bdba Mon Sep 17 00:00:00 2001
From: Ryan Hendrickson <ryan.hendrickson@alum.mit.edu>
Date: Thu, 22 Oct 2020 01:11:14 -0400
Subject: [PATCH 1/2] Fix `Foldable1 (NonEmpty f)` instance

---
 src/Data/NonEmpty.purs | 11 +++++------
 test/Main.purs         |  5 +++--
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/src/Data/NonEmpty.purs b/src/Data/NonEmpty.purs
index 957b88c..c51cc3e 100644
--- a/src/Data/NonEmpty.purs
+++ b/src/Data/NonEmpty.purs
@@ -4,11 +4,11 @@ module Data.NonEmpty
   ( NonEmpty(..)
   , singleton
   , (:|)
-  , foldl1
   , fromNonEmpty
   , oneOf
   , head
   , tail
+  , module Exports
   ) where
 
 import Prelude
@@ -20,9 +20,10 @@ import Data.Eq (class Eq1)
 import Data.Foldable (class Foldable, foldl, foldr, foldMap)
 import Data.FoldableWithIndex (class FoldableWithIndex, foldMapWithIndex, foldlWithIndex, foldrWithIndex)
 import Data.FunctorWithIndex (class FunctorWithIndex, mapWithIndex)
-import Data.Maybe (Maybe(..))
+import Data.Maybe (Maybe(..), maybe)
 import Data.Ord (class Ord1)
 import Data.Semigroup.Foldable (class Foldable1, foldMap1)
+import Data.Semigroup.Foldable (foldl1) as Exports
 import Data.Traversable (class Traversable, traverse, sequence)
 import Data.TraversableWithIndex (class TraversableWithIndex, traverseWithIndex)
 import Data.Tuple (uncurry)
@@ -46,10 +47,6 @@ infixr 5 NonEmpty as :|
 singleton :: forall f a. Plus f => a -> NonEmpty f a
 singleton a = a :| empty
 
--- | Fold a non-empty structure, collecting results using a binary operation.
-foldl1 :: forall f a. Foldable f => (a -> a -> a) -> NonEmpty f a -> a
-foldl1 f (a :| fa) = foldl f a fa
-
 fromNonEmpty :: forall f a r. (a -> f a -> r) -> NonEmpty f a -> r
 fromNonEmpty f (a :| fa) = a `f` fa
 
@@ -107,6 +104,8 @@ instance traversableWithIndexNonEmpty
 instance foldable1NonEmpty :: Foldable f => Foldable1 (NonEmpty f) where
   fold1 = foldMap1 identity
   foldMap1 f (a :| fa) = foldl (\s a1 -> s <> f a1) (f a) fa
+  foldr1 f (a :| fa) = maybe a (f a) $ foldr (\a1 -> Just <<< maybe a1 (f a1)) Nothing fa
+  foldl1 f (a :| fa) = foldl f a fa
 
 instance unfoldable1NonEmpty :: Unfoldable f => Unfoldable1 (NonEmpty f) where
   unfoldr1 f b = uncurry (:|) $ unfoldr (map f) <$> f b
diff --git a/test/Main.purs b/test/Main.purs
index b0a7e9a..9e3fcac 100644
--- a/test/Main.purs
+++ b/test/Main.purs
@@ -5,7 +5,7 @@ import Prelude
 import Data.Foldable (fold, foldl)
 import Data.Maybe (Maybe(..))
 import Data.NonEmpty (NonEmpty, (:|), foldl1, oneOf, head, tail, singleton)
-import Data.Semigroup.Foldable (fold1)
+import Data.Semigroup.Foldable (fold1, foldr1)
 import Data.Unfoldable1 as U1
 import Effect (Effect)
 import Test.Assert (assert)
@@ -19,7 +19,8 @@ main :: Effect Unit
 main = do
   assert $ singleton 0 == 0 :| []
   assert $ 0 :| Nothing /= 0 :| Just 1
-  assert $ foldl1 (+) (1 :| [2, 3]) == 6
+  assert $ foldl1 (\l r -> "(" <> l <> r <> ")") ("a" :| ["b", "c", "d"]) == "(((ab)c)d)"
+  assert $ foldr1 (\l r -> "(" <> l <> r <> ")") ("a" :| ["b", "c", "d"]) == "(a(b(cd)))"
   assert $ foldl (+) 0 (1 :| [2, 3]) == 6
   assert $ fold1 ("Hello" :| [" ", "World"]) == "Hello World"
   assert $ fold ("Hello" :| [" ", "World"]) == "Hello World"

From 4e363202e02ab9406933a54a026484ea3fa7b7b7 Mon Sep 17 00:00:00 2001
From: Ryan Hendrickson <ryan.hendrickson@alum.mit.edu>
Date: Thu, 22 Oct 2020 18:46:26 -0400
Subject: [PATCH 2/2] fixup! Fix `Foldable1 (NonEmpty f)` instance

---
 src/Data/NonEmpty.purs | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/src/Data/NonEmpty.purs b/src/Data/NonEmpty.purs
index c51cc3e..9e5f75a 100644
--- a/src/Data/NonEmpty.purs
+++ b/src/Data/NonEmpty.purs
@@ -4,11 +4,11 @@ module Data.NonEmpty
   ( NonEmpty(..)
   , singleton
   , (:|)
+  , foldl1
   , fromNonEmpty
   , oneOf
   , head
   , tail
-  , module Exports
   ) where
 
 import Prelude
@@ -23,7 +23,6 @@ import Data.FunctorWithIndex (class FunctorWithIndex, mapWithIndex)
 import Data.Maybe (Maybe(..), maybe)
 import Data.Ord (class Ord1)
 import Data.Semigroup.Foldable (class Foldable1, foldMap1)
-import Data.Semigroup.Foldable (foldl1) as Exports
 import Data.Traversable (class Traversable, traverse, sequence)
 import Data.TraversableWithIndex (class TraversableWithIndex, traverseWithIndex)
 import Data.Tuple (uncurry)
@@ -47,6 +46,10 @@ infixr 5 NonEmpty as :|
 singleton :: forall f a. Plus f => a -> NonEmpty f a
 singleton a = a :| empty
 
+-- | Fold a non-empty structure, collecting results using a binary operation.
+foldl1 :: forall f a. Foldable f => (a -> a -> a) -> NonEmpty f a -> a
+foldl1 f (a :| fa) = foldl f a fa
+
 fromNonEmpty :: forall f a r. (a -> f a -> r) -> NonEmpty f a -> r
 fromNonEmpty f (a :| fa) = a `f` fa
 
@@ -105,7 +108,7 @@ instance foldable1NonEmpty :: Foldable f => Foldable1 (NonEmpty f) where
   fold1 = foldMap1 identity
   foldMap1 f (a :| fa) = foldl (\s a1 -> s <> f a1) (f a) fa
   foldr1 f (a :| fa) = maybe a (f a) $ foldr (\a1 -> Just <<< maybe a1 (f a1)) Nothing fa
-  foldl1 f (a :| fa) = foldl f a fa
+  foldl1 = foldl1
 
 instance unfoldable1NonEmpty :: Unfoldable f => Unfoldable1 (NonEmpty f) where
   unfoldr1 f b = uncurry (:|) $ unfoldr (map f) <$> f b