From e99ecb8b3f98a5e4ececde9b72d7e39e6609690a Mon Sep 17 00:00:00 2001
From: Shane <me@shane.sh>
Date: Tue, 28 Apr 2020 12:39:32 +0100
Subject: [PATCH] semialign: Generalize {l,r}padZip to work on any Semialign
 container that is Filterable

This introduces a dependency on witherable-class. It's a small package and we already depend on all of its dependencies.
---
 semialign/semialign.cabal                |  1 +
 semialign/src/Data/Semialign/Internal.hs | 10 +++++-----
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/semialign/semialign.cabal b/semialign/semialign.cabal
index 0777065..6d56f02 100644
--- a/semialign/semialign.cabal
+++ b/semialign/semialign.cabal
@@ -75,6 +75,7 @@ library
     , tagged                >=0.8.6    && <0.9
     , unordered-containers  >=0.2.8.0  && <0.3
     , vector                >=0.12.0.2 && <0.13
+    , witherable-class      >=0        && <0.1
 
   -- base shims
   if !impl(ghc >=8.2)
diff --git a/semialign/src/Data/Semialign/Internal.hs b/semialign/src/Data/Semialign/Internal.hs
index 7f07ebf..803ba12 100644
--- a/semialign/src/Data/Semialign/Internal.hs
+++ b/semialign/src/Data/Semialign/Internal.hs
@@ -17,13 +17,13 @@ import Data.Functor.Product              (Product (..))
 import Data.Hashable                     (Hashable (..))
 import Data.HashMap.Strict               (HashMap)
 import Data.List.NonEmpty                (NonEmpty (..))
-import Data.Maybe                        (catMaybes)
 import Data.Proxy                        (Proxy (..))
 import Data.Semigroup                    (Option (..), Semigroup (..))
 import Data.Sequence                     (Seq)
 import Data.Tagged                       (Tagged (..))
 import Data.Vector.Fusion.Stream.Monadic (Step (..), Stream (..))
 import Data.Vector.Generic               (Vector, empty, stream, unstream)
+import Data.Witherable.Class             (Filterable, catMaybes)
 
 import qualified Data.HashMap.Strict               as HM
 import qualified Data.List.NonEmpty                as NE
@@ -744,17 +744,17 @@ padZipWith :: (Semialign f) => (Maybe a -> Maybe b -> c) -> f a -> f b -> f c
 padZipWith f xs ys = uncurry f <$> padZip xs ys
 
 -- | Left-padded 'zipWith'.
-lpadZipWith :: (Maybe a -> b -> c) -> [a] -> [b] -> [c]
+lpadZipWith :: (Semialign f, Filterable f) => (Maybe a -> b -> c) -> f a -> f b -> f c
 lpadZipWith f xs ys = catMaybes $ padZipWith (\x y -> f x <$> y) xs ys
 
 -- | Left-padded 'zip'.
-lpadZip :: [a] -> [b] -> [(Maybe a, b)]
+lpadZip :: (Semialign f, Filterable f) => f a -> f b -> f (Maybe a, b)
 lpadZip = lpadZipWith (,)
 
 -- | Right-padded 'zipWith'.
-rpadZipWith :: (a -> Maybe b -> c) -> [a] -> [b] -> [c]
+rpadZipWith :: (Semialign f, Filterable f) => (a -> Maybe b -> c) -> f a -> f b -> f c
 rpadZipWith f xs ys = lpadZipWith (flip f) ys xs
 
 -- | Right-padded 'zip'.
-rpadZip :: [a] -> [b] -> [(a, Maybe b)]
+rpadZip :: (Semialign f, Filterable f) => f a -> f b -> f (a, Maybe b)
 rpadZip = rpadZipWith (,)