Re: [Haskell-cafe] Re: Wikipedia on first-class object

On 12/30/07, Cristian Baboi 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