> However, the definition of bracket relies on block and
> unblock, which have the
> following types:
> > bracket :: IO a -> (a -> IO b) -> (a -> IO c) -> IO c
> > block :: IO a -> IO a
> > unblock :: IO a -> IO a
>
> This forces f to be an IO action in the above withQuery
> function. If bracket,
> block, and unblock had these types, my helper function would
> be well typed:
>
> > bracket :: MonadIO m => m a -> (a -> m b) -> (a -> m c) -> m c
> > block :: MonadIO m => m a -> m a
> > unblock :: MonadIO m => m a -> m a
>
> Would anything prevent block, unblock, bracket (and other
> similar functions
> working on IO actions) from being generalized to all intances
> of MonadIO?
I'm afraid I can't see a way to generalise the types of block and
unblock, since they are based on underlying primitives that really do
have type (IO a -> IO a). Perhaps if your monad is isomorphic to IO, it
could be done, but otherwise I don't think it's possible. Unless I'm
missing something.
Cheers,
Simon
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