Use external strict pair package (use strict-tuple-lens also?)

src/FoldlHelp.hs

@@ -1,13 +1,15 @@
-module FoldlHelp
+module FoldlHelp (
-    ( minimumOn
+    minimumOn,
-    , premapMaybe
+    premapMaybe,
-    , module Control.Foldl
+    module Control.Foldl,
-    ) where
+) where
+
 import Control.Foldl
 import MaybeHelp
+import Data.Strict.Tuple
 
 --data Maybe' a = Just' !a | Nothing'
-data Pair a b = !a :!: !b
+--data Pair a b = !a :!: !b
 
 minimumOn :: Ord b => (a -> b) -> Fold a (Maybe a)
 minimumOn f = Fold step Nothing' extract
@@ -16,15 +18,15 @@ minimumOn f = Fold step Nothing' extract
     extract (Just' (a :!: _)) = Just a
     step Nothing' b = Just' (b :!: f b)
     step (Just' (a :!: x)) b
-        | y < x     = Just' (b :!: y)
+        | y < x = Just' (b :!: y)
         | otherwise = Just' (a :!: x)
       where
         y = f b
 
 premapMaybe :: (a -> Maybe b) -> Fold b r -> Fold a r
-{-# INLINABLE premapMaybe #-}
+{-# INLINEABLE premapMaybe #-}
 premapMaybe f (Fold step initial extract) = Fold step' initial extract
   where
     step' x a = case f a of
         Nothing -> x
-        Just s  -> step x s
+        Just s -> step x s