blob: 081dc3643bce62ea467acd45e74df937511fa8fe (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
|
{-# LANGUAGE GADTs #-}
module Main where
import Data.IORef
data T a where
Li:: Int -> T Int
Lb:: Bool -> T Bool
La:: a -> T a
writeInt:: T a -> IORef a -> IO ()
writeInt v ref = case v of
~(Li x) -> writeIORef ref (1::Int)
readBool:: T a -> IORef a -> IO ()
readBool v ref = case v of
~(Lb x) ->
readIORef ref >>= (print . not)
tt::T a -> IO ()
tt v = case v of
~(Li x) -> print "OK"
main = do
tt (La undefined)
ref <- newIORef undefined
writeInt (La undefined) ref
readBool (La undefined) ref
|
