Property.hs

{-# LANGUAGE TypeSynonymInstances #-}
{-# LANGUAGE FlexibleInstances #-}
module Affection.Property 
  ( Props
  , prop
  , props
  ) where

import qualified GEGL as G
import qualified BABL as B

import Control.Monad.State.Lazy
import Foreign.Ptr (Ptr)

type Props a = State [G.Property] a

props :: Props a -> [G.Property]
props = flip execState []

prop :: IsPropertyValue v => String -> v -> Props ()
prop k v = do
  ps <- get
  put $ G.Property k (toPropertyValue v) : ps

class IsPropertyValue v where
  toPropertyValue :: v -> G.PropertyValue

instance IsPropertyValue Int where
  toPropertyValue = G.PropertyInt

instance IsPropertyValue String where
  toPropertyValue = G.PropertyString

instance IsPropertyValue Double where
  toPropertyValue = G.PropertyDouble

instance IsPropertyValue G.Color where
  toPropertyValue = G.PropertyColor

instance IsPropertyValue B.PixelFormat where
  toPropertyValue = G.PropertyFormat
instance IsPropertyValue G.GeglBuffer where
  toPropertyValue = G.PropertyBuffer

instance IsPropertyValue (Ptr ()) where
  toPropertyValue = G.PropertyPointer