Language/Symantic/Expr/Root.hs

   1 {-# LANGUAGE ConstraintKinds #-}
   2 {-# LANGUAGE DataKinds #-}
   3 {-# LANGUAGE FlexibleContexts #-}
   4 {-# LANGUAGE FlexibleInstances #-}
   5 {-# LANGUAGE GADTs #-}
   6 {-# LANGUAGE KindSignatures #-}
   7 {-# LANGUAGE MultiParamTypeClasses #-}
   8 {-# LANGUAGE Rank2Types #-}
   9 {-# LANGUAGE ScopedTypeVariables #-}
  10 {-# LANGUAGE TypeFamilies #-}
  11 {-# LANGUAGE TypeOperators #-}
  12 {-# LANGUAGE UndecidableInstances #-}
  13 module Language.Symantic.Expr.Root where
  14
  15 import Language.Symantic.Type
  16
  17 -- * Type 'Expr_Root'
  18 -- | The root expression, passing itself as parameter to the given expression.
  19 newtype Expr_Root (ex:: * -> *)
  20  =      Expr_Root (ex (Expr_Root ex))
  21 type instance Root_of_Expr (Expr_Root ex) = Expr_Root ex
  22 type instance Type_of_Expr (Expr_Root ex)
  23  =            Type_of_Expr (ex (Expr_Root ex))
  24
  25 -- * Type family 'Root_of_Expr'
  26 -- | The root expression of an expression.
  27 type family Root_of_Expr (ex:: *) :: *
  28
  29 -- * Type family 'Type_of_Expr'
  30 -- | The type of an expression, parameterized by a root type.
  31 type family Type_of_Expr (ex:: *) :: {-root-}(* -> *) -> {-h-}* -> *
  32
  33 -- ** Type 'Type_Root_of_Expr'
  34 -- | Convenient alias.
  35 --
  36 -- NOTE: include 'Type_Var' only to use it
  37 -- within 'Error_Expr_Type_mismatch' so far.
  38 type Type_Root_of_Expr (ex:: *)
  39  =   Type_Root (Type_Var0 :|: Type_Var1 :|: Type_of_Expr (Root_of_Expr ex))