purescript-default-args.purs

module DefArgs
( Vec4 (..)
, ToVec4
, toVec4
) where

data Vec4 = Vec4 Number Number Number Number

instance showVec4 :: Show Vec4 where
  show (Vec4 x y z t) =
    "(Vec4 " ++
    show x ++ " " ++
    show y ++ " " ++
    show z ++ " " ++
    show t ++ ")"

class ToVec4 a where
  toVec4 :: a -> Vec4

instance toVec4AllArgs :: ToVec4 Vec4 where
  toVec4 = id

instance toVec4With3Args :: ToVec4 (Number -> Vec4) where
  toVec4 f = f 1

instance toVec4With2Args :: ToVec4 (Number -> Number -> Vec4) where
  toVec4 f = f 0 1
  
{-
  toVec4 $ Vec4 3 2 1 5
  => (Vec4 3 2 1 5)
  
  toVec4 $ Vec4 3 2
  => (Vec4 3 2 0 1)
-}