Would a specialization of return work, as in f = return :: Maybe a -> IO (Maybe a)? On Mon, Sep 4, 2017 at 7:00 AM, <beginners-request@haskell.org> wrote:
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Today's Topics:
1. I have a -> f a. How to get m a -> f m a ? (Baa) 2. Re: I have a -> f a. How to get m a -> f m a ? (Imants Cekusins)
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Message: 1 Date: Mon, 4 Sep 2017 15:06:34 +0300 From: Baa <aquagnu@gmail.com> To: beginners@haskell.org Subject: [Haskell-beginners] I have a -> f a. How to get m a -> f m a ? Message-ID: <20170904150634.230dd5ff@Pavel> Content-Type: text/plain; charset=US-ASCII
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 <$> myfunc x'
but more interesting is to know more standard and Haskelish solution (like lift's, etc). May be I miss something very obvious..
=== Best regards, Paul
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Message: 2 Date: Mon, 4 Sep 2017 15:14:42 +0300 From: Imants Cekusins <imantc@gmail.com> To: The Haskell-Beginners Mailing List - Discussion of primarily beginner-level topics related to Haskell <beginners@haskell.org> Subject: Re: [Haskell-beginners] I have a -> f a. How to get m a -> f m a ? Message-ID: <CAP1qinaEhE6HqvS0O9-CfV9Vc2x8ZvfQ_SRFXQgVH- yhapZZtg@mail.gmail.com> Content-Type: text/plain; charset="utf-8"
I have function a -> IO a. How to get function: Maybe a -> IO (Maybe a) ?
Will mapM work:
http://hackage.haskell.org/package/base-4.10.0.0/docs/ Data-Traversable.html#v:mapM
?
On 4 September 2017 at 15:06, Baa <aquagnu@gmail.com> wrote:
Hello List!
I have function a -> IO a. How to get function:
Maybe a -> IO (Maybe a) ?
I found in Haskell mails archive such thing:
class IFunctor f where imap :: Idiom i => (s -> i t) -> f s -> i (f t)
which looks similar, but I didn't find any helpfull instances of `IFunctor` class in its package (and unfortunately I don't know what are the indexed types: IMonad, IFunctor, etc). Sure, there is the primitive solution like:
myfunc :: a -> IO a ... f x = case x of Nothing -> return Nothing Just x' -> Just <$> 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 _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners