cli/Hcompta/Expr/Trans.hs

   1 {-# LANGUAGE FlexibleInstances #-}
   2 {-# LANGUAGE MultiParamTypeClasses #-}
   3 {-# LANGUAGE NoImplicitPrelude #-}
   4
   5 module Hcompta.Expr.Trans where
   6
   7 import Data.Function ((.))
   8
   9 -- |
  10 -- * 'trans_lift' is generally not /surjective/
  11 -- * 'trans_apply' is not /injective/
  12 -- * 'trans_apply' . 'trans_lift' == 'id'
  13 -- * 'trans_lift' . 'trans_apply' /= 'id'
  14 class Trans trans repr where
  15         trans_lift  :: repr a -> trans repr a
  16         trans_apply :: trans repr a -> repr a
  17
  18         trans_map1 :: (repr a -> repr b) -> (trans repr a -> trans repr b)
  19         trans_map1 f = trans_lift . f . trans_apply
  20
  21         trans_map2
  22          :: (repr a -> repr b -> repr c)
  23          -> (trans repr a -> trans repr b -> trans repr c)
  24         trans_map2 f e1 e2 = trans_lift (f (trans_apply e1) (trans_apply e2))