simpalg.hs

{-# LANGUAGE DeriveFunctor #-}

data ExprF r = Const Int
             | Add r r
             | Mul r r
    deriving Functor

newtype Fix f = Fx (f (Fix f))

val :: Fix ExprF
val = Fx (Const 12)

testExpr = Fx $ (Fx $ (Fx $ Const 2) `Add` 
                (Fx $ Const 3)) `Mul` (Fx $ Const 4)

p = Const 12
main = return ()