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

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#... ? On 4 September 2017 at 15:06, Baa 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 _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners