Merge pull request #106 from purescript/more-fn-instances

Add more instances of the form `C b => C (a -> b)`

Author: garyb

src/Data/BooleanAlgebra.purs

@@ -18,3 +18,4 @@ class HeytingAlgebra a <= BooleanAlgebra a
 
 instance booleanAlgebraBoolean :: BooleanAlgebra Boolean
 instance booleanAlgebraUnit :: BooleanAlgebra Unit
+instance booleanAlgebraFn :: BooleanAlgebra b => BooleanAlgebra (a -> b)

src/Data/CommutativeRing.purs

@@ -20,3 +20,4 @@ class Ring a <= CommutativeRing a
 instance commutativeRingInt :: CommutativeRing Int
 instance commutativeRingNumber :: CommutativeRing Number
 instance commutativeRingUnit :: CommutativeRing Unit
+instance commutativeRingFn :: CommutativeRing b => CommutativeRing (a -> b)

src/Data/Ring.purs

@@ -27,6 +27,9 @@ instance ringNumber :: Ring Number where
 instance ringUnit :: Ring Unit where
   sub _ _ = unit
 
+instance ringFn :: Ring b => Ring (a -> b) where
+  sub f g x = f x - g x
+
 -- | `negate x` can be used as a shorthand for `zero - x`.
 negate :: forall a. Ring a => a -> a
 negate a = zero - a

src/Data/Semiring.purs

@@ -44,6 +44,12 @@ instance semiringNumber :: Semiring Number where
   mul = numMul
   one = 1.0
 
+instance semiringFn :: Semiring b => Semiring (a -> b) where
+  add f g x = f x + g x
+  zero = \_ -> zero
+  mul f g x = f x * g x
+  one = \_ -> one
+
 instance semiringUnit :: Semiring Unit where
   add _ _ = unit
   zero = unit