Re: [Haskell-cafe] The Q Programming Language can do symbolic manipulation -- Haskell?

16 Aug 2006

      On 8/16/06, Casey Hawthorne  wrote:
...
The Q Programming Language can do symbolic manipulation -- Haskell?
The Q Programming Language can do the following:
sqr X = X*X
==>sqr 5
25
==>sqr (X+1)
(X+1)*(X+1)
Can Haskell do symbolic manipulation?
Or are term-rewriting and the lambda calculus sufficiently far enough
apart concepts?
You can do (if you don't mind cheating) :

Compiling Sym              ( Sym.hs, interpreted )
:Ok, modules loaded: Sym.
*Sym> :!cat Sym.hs
module Sym where

data Sym a = Const a
           | Var String
           | Sym a `Mult` Sym a
           | Sym a `Plus` Sym a
           | Sym a `Minus` Sym a
             deriving (Eq,Show)

instance Num a => Num (Sym a) where
    (+) = Plus
    (*) = Mult
    abs = id
    signum = id
    fromInteger = Const . fromInteger

sqr x = x*x

*Sym> sqr 5
25
*Sym> sqr (Var "X" + 1)
(Var "X" Plus Const 1) Mult (Var "X" Plus Const 1)

-- 
Cheers,
  Lemmih