[Haskell-beginners] I have a -> f a. How to get m a -> f m a ?

[Imants Cekusins]

> I have function a -> IO a. How to get function:
>  Maybe a -> IO (Maybe a)  ?

Will mapM work:

http://hackage.haskell.org/package/base-4.10.0.0/docs/Data-Traversable.html#v:mapM

?



On 4 September 2017 at 15:06, Baa <aquagnu at gmail.com> wrote:

> Hello List!
>
> I have function a -> IO a. How to get function:
>
>   Maybe a -> IO (Maybe a)  ?
>
> I found in Haskell mails archive such thing:
>
>    class IFunctor f where
>      imap :: Idiom i => (s -> i t) -> f s -> i (f t)
>
> which looks similar, but I didn't find any helpfull instances of
> `IFunctor` class in its package (and unfortunately I don't know what are
> the indexed types: IMonad, IFunctor, etc). Sure, there is the primitive
> solution like:
>
>    myfunc :: a -> IO a
>    ...
>    f x = case x of Nothing -> return Nothing
>                    Just x' -> Just <$> myfunc x'
>
> but more interesting is to know more standard and Haskelish solution
> (like lift's, etc). May be I miss something very obvious..
>
> ===
> Best regards, Paul
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>
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