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

apfelmus at quantentunnel.de apfelmus at quantentunnel.de
Sat Feb 3 04:13:17 EST 2007

Chad Scherrer wrote:
> Unfortunately, I was trying to give a simplification of the real
> problem, where the monad is STM instead of []. Based on apfelmus's
> observation of why they can't be isomorphic, I'm guessing I'm out of
> luck.
> http://www.haskell.org/pipermail/haskell-cafe/2006-December/020041.html
> So in reality, I'm trying to construct something like
> f :: (a -> STM b) -> STM (a -> b)

Indeed, such an f most likely does not exist. What is the task you tried
to solve with the help of f? I guess that either there is a way without
or it just cannot be solved for mathematical reasons.


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