[Haskell-cafe] (a -> [b]) vs. [a -> b]

[J. Garrett Morris]

On 2/2/07, Chad Scherrer <chad.scherrer at gmail.com> wrote:
> So in reality, I'm trying to construct something like
> f :: (a -> STM b) -> STM (a -> b)
>
> I just figured it was a general monadic kind of problem, more simply
> expressed using lists. But the (!!) solution doesn't make sense in
> this context.

Perhaps this will work for you:

f x = join . liftM f

This typechecks, and seems to work as expected, e.g.:

Prelude Control.Concurrent.STM Control.Monad> atomically (f readTVar
(newTVar 'a'))
'a'

 /g

-- 
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