Add PureScript language & samples

samples/PureScript/Control.Arrow.purs

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+module Control.Arrow where
+
+import Data.Tuple
+
+class Arrow a where
+  arr :: forall b c. (b -> c) -> a b c
+  first :: forall b c d. a b c -> a (Tuple b d) (Tuple c d)
+
+instance arrowFunction :: Arrow (->) where
+  arr f = f
+  first f (Tuple b d) = Tuple (f b) d
+
+second :: forall a b c d. (Category a, Arrow a) => a b c -> a (Tuple d b) (Tuple d c)
+second f = arr swap >>> first f >>> arr swap
+
+swap :: forall a b. Tuple a b -> Tuple b a
+swap (Tuple x y) = Tuple y x
+
+infixr 3 ***
+infixr 3 &&&
+
+(***) :: forall a b b' c c'. (Category a, Arrow a) => a b c -> a b' c' -> a (Tuple b b') (Tuple c c')
+(***) f g = first f >>> second g
+
+(&&&) :: forall a b b' c c'. (Category a, Arrow a) => a b c -> a b c' -> a b (Tuple c c')
+(&&&) f g = arr (\b -> Tuple b b) >>> (f *** g)
+
+class ArrowZero a where
+  zeroArrow :: forall b c. a b c
+
+infixr 5 <+>
+
+class ArrowPlus a where
+  (<+>) :: forall b c. a b c -> a b c -> a b c