[Haskell-beginners] Doing IO in terms of Arrow

[Haisheng Wu]

You find point I need the correct type signatures.
And seems like it is (missed IO in your description)
Kleisli IO FilePath [FilePath]

Thanks a lot!

-Haisheng


On Tue, Jun 28, 2011 at 12:38 AM, Ertugrul Soeylemez <es at ertes.de> wrote:

> Haisheng Wu <freizl at gmail.com> wrote:
>
> >   I'm wondering if it is possible doing IO in terms of Arrow.
> >   I got a function search all files under directory recursively and
> > I'd like to refartoring using Arrow terms.
>
> Yes, it's possible using Kleisli, but it's not very convenient, because
> you need the Kleisli wrapper around everything.  Also usually there is
> really little reason to do that, because monads are more expressive.
> For example they allow you to encode computations with only outputs
> directly, without wrapping them in a computation, which takes a stub
> argument.
>
>
> >   I tried to define a function like below but failed.
> >   isDirExist = Kleisli doesDirectoryExist
> >
> >   Do I need to define a instance for IO to be Arrow? Or is there any
> > existing solutions?
>
> No, the needed instances are already there, but you need to change your
> type signatures:
>
>    myGetFilesInDir :: Kleisli FilePath [FilePath]
>
>
> Greets,
> Ertugrul
>
>
> --
> nightmare = unsafePerformIO (getWrongWife >>= sex)
> http://ertes.de/
>
>
>
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