Created
July 27, 2010 15:16
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{-# LANGUAGE GADTs #-} | |
{-# LANGUAGE StandaloneDeriving #-} | |
module GADTExpr where | |
import Data.Function(on) | |
import Data.Ord(comparing) | |
class (Eq a, Ord a, Show a) => ExprType a where | |
toExpr :: a -> Expr a | |
instance ExprType Bool where toExpr = Bin | |
instance ExprType Int where toExpr = Num | |
data Expr a where | |
Bin :: Bool -> Expr Bool | |
Num :: Int -> Expr Int | |
(:+:) :: Expr Int -> Expr Int -> Expr Int | |
(:-:) :: Expr Int -> Expr Int -> Expr Int | |
(:=:) :: ExprType a => Expr a -> Expr a -> Expr Bool | |
(:<:) :: ExprType a => Expr a -> Expr a -> Expr Bool | |
(:/\:) :: Expr Bool -> Expr Bool -> Expr Bool | |
(:\/:) :: Expr Bool -> Expr Bool -> Expr Bool | |
instance Eq (Expr a) where (==) = (==) `on` show | |
instance Ord (Expr a) where compare = comparing show | |
deriving instance Show (Expr a) | |
eval :: ExprType a => Expr a -> Expr a | |
eval = toExpr . evalExpr | |
evalExpr :: ExprType a => Expr a -> a | |
evalExpr (Bin i) = i | |
evalExpr (Num i) = i | |
evalExpr (a :+: b) = evalExpr a + evalExpr b | |
evalExpr (a :-: b) = evalExpr a - evalExpr b | |
evalExpr (a :=: b) = evalExpr a == evalExpr b | |
evalExpr (a :<: b) = evalExpr a < evalExpr b | |
transform :: (ExprType a, ExprType b) => (Expr b -> Expr b) -> Expr a -> Expr a | |
transform = undefined |
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