Thanks. So GADT provide us to generic type to include all types, is it right? ex: data Parser tok a where Zero :: Parser tok () One :: Parser tok () Check :: (tok -> Bool) -> Parser tok tok Satisfy :: ([tok] -> Bool) -> Parser tok [tok] Push :: tok -> Parser tok a -> Parser tok a Plus :: Parser tok a -> Parser tok b -> Parser tok (Either a b) Times :: Parser tok a -> Parser tok b -> Parser tok (a,b) Star :: Parser tok a -> Parser tok [a] otherwise we need to write something like this (separate the type and functions): newtype Parser tok a zero::Parser tok () one :: Parser tok () ... On Nov 27, 2007 2:16 PM, Luke Palmer <lrpalmer@gmail.com> wrote:
On Nov 27, 2007 12:57 PM, Yu-Teh Shen <shenyute@gmail.com> wrote:
i have seen the documents in http://www.haskell.org/haskellwiki/Generalised_algebraic_datatype but i can not run the following code on ghci
ex:
data Term x where K :: Term (a -> b -> a) S :: Term ((a -> b -> c) -> (a -> b) -> a -> c) Const :: a -> Term a (:@) :: Term (a -> b) -> (Term a) -> Term b infixl 6 :@
could any tell me how to run the code?
Put it in a file (eg ski.hs), and run:
% ghci -fglasgow-exts ski.hs
You cannot enter it directly into ghci; you can't define new data types interactively.
You can also put the line
{-# OPTIONS_GHC -fglasgow-exts #-}
At the top, to turn on glasgow extensions whenever GHC compiles this file.
Luke