On 12/30/07, Cristian Baboi <cristi@ot.onrc.ro> wrote:

Thank you.

data Something = This | S Something

ppp :: Something -> String

ppp This = ""
ppp (S x) = 'S':(ppp x)

How can I prevent one to pass 'let x = S x in x' to ppp ?

{-# LANGUAGE GADTs, EmptyDataDecls #-}

data Z

data S a

data Something a where

This :: Something Z

S :: Something a -> Something (S a)

ppp :: Something a -> String

ppp This = ""

ppp (S x) = 'S' : ppp x