Language/Symantic/Trans/Common.hs

   1 {-# LANGUAGE MultiParamTypeClasses #-}
   2 module Language.Symantic.Trans.Common where
   3
   4 -- |
   5 -- * 'trans_lift' is generally not /surjective/
   6 -- * 'trans_apply' is not /injective/
   7 -- * 'trans_apply' . 'trans_lift' == 'id'
   8 -- * 'trans_lift' . 'trans_apply' /= 'id'
   9 --
  10 -- NOTE: @DefaultSignatures@ can be used
  11 -- when declaring a symantic type class
  12 -- to provide default definition of the methods
  13 -- implementing their identity transformation
  14 -- in order to avoid boilerplate code
  15 -- when writting 'Trans' instances which
  16 -- do not need to alterate those methods.
  17 class Trans trans repr where
  18         -- | Lift an interpreter to the transformer's.
  19         trans_lift  :: repr a -> trans repr a
  20         -- | Unlift an interpreter from the transformer's.
  21         trans_apply :: trans repr a -> repr a
  22
  23         -- | Convenient method to define the identity transformation for a unary symantic method.
  24         trans_map1 :: (repr a -> repr b) -> (trans repr a -> trans repr b)
  25         trans_map1 f = trans_lift . f . trans_apply
  26
  27         -- | Convenient method to define the identity transformation for a binary symantic method.
  28         trans_map2
  29          :: (repr a -> repr b -> repr c)
  30          -> (trans repr a -> trans repr b -> trans repr c)
  31         trans_map2 f e1 e2 = trans_lift (trans_apply e1 `f` trans_apply e2)
  32
  33         -- | Convenient method to define the identity transformation for a terary symantic method.
  34         trans_map3
  35          :: (repr a -> repr b -> repr c -> repr d)
  36          -> (trans repr a -> trans repr b -> trans repr c -> trans repr d)
  37         trans_map3 f e1 e2 e3 = trans_lift $ f (trans_apply e1) (trans_apply e2) (trans_apply e3)