At 2002-02-20 22:15, I wrote (on the Haskell list):
>Haskell? Given this:
>
> class (Monad m) => PeirceMonad m where
> {
> peirceM :: ((a -> m b) -> m a) -> m a;
> };
>
>...which Monads can be made PeirceMonads?
This is untested, but...
instance PeirceMonad IO where
{
peirceM foo = do
{
ref <- newIORef Nothing;
catch (foo (\a -> do
{
writeIORef ref (Just a);
ioError (userError "break");
}))
(\ex -> do
{
ma <- readIORef ref;
case ma of
{
Just a -> return a;
_ -> ioError ex;
};
})
}
};
So you can do it if you have refs and throw/catch for your monad. I think.
--
Ashley Yakeley, Seattle WA
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