Add knightDeltas.hs

dotfiles/lib/bin/knightDeltas.hs

@@ -0,0 +1,22 @@
+#!/usr/bin/env run_haskell_stack.sh
+
+import Data.Bifunctor
+import Data.Tuple
+
+knightDeltasSimple =
+  applyAll [swap] (1, 2)
+  >>= applyAll [first negate, second negate, bimapBoth negate]
+  where applyAll fns v = map ($ v) $ id:fns
+        bimapBoth fn = bimap fn fn
+
+knightDeltas = applyInStages [(1, 2)]
+               [ [swap]
+               , [bimapBoth (* 2)]
+               , [first negate, second negate, bimapBoth negate]
+               ]
+  where applyAll fns v = map ($ v) $ id:fns
+        applyAllToValues values fns = values >>= applyAll fns
+        applyInStages = foldl applyAllToValues
+        bimapBoth fn = bimap fn fn
+
+main = print knightDeltas