mapMaybeM

[andrewthad]

Can I add mapMaybeM to vector? The type signature would be:

mapMaybeM :: (a -> m (Maybe b)) -> Vector a -> m (Vector b)

Although the list-equivalent of mapMaybeM is not in base, it's a pretty common thing for people to write. I can see from some googling that it exists in monad-extras, extra, and in stack. I bring this up because I think it highlights the utility of such a function and the common expected semantics people seem to have for it.

[cartazio]

Have you seen the witherable package?

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On Tue, Aug 29, 2017 at 10:13 AM Andrew Martin ***@***.***> wrote: Can I add mapMaybeM to vector? The type signature would be: mapMaybeM :: (a -> m (Maybe b)) -> Vector a -> m (Vector b) Although the list-equivalent of mapMaybeM is not in base, it's a pretty common thing for people to write. I can see from some googling that it exists in monad-extras <https://hackage.haskell.org/package/monad-extras-0.6.0/docs/Control-Monad-Extra.html#v:mapMaybeM>, extra <https://hackage.haskell.org/package/extra-1.6/docs/Control-Monad-Extra.html#v:mapMaybeM>, and in stack <https://hackage.haskell.org/package/stack-1.0.0/docs/src/Data.Maybe.Extra.html>. I bring this up because I think it highlights the utility of such a function and the common expected semantics people seem to have for it. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#183>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAAQwsq4PplMJdQOTB0QpMvTg2edcbgfks5sdBx7gaJpZM4PGAYH> .

[andrewthad]

I have. Still, a more direct definition of mapMaybeM would be more efficient that using witherM.

[cartazio]

Sorry... what do you mean by more definition ?

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On Tue, Aug 29, 2017 at 7:24 PM Andrew Martin ***@***.***> wrote: I have. Still, the more definition of mapMaybeM would be more efficient that using witherM. — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#183 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAAQwlQT105_I9lhnIWKte0lVisQYpOwks5sdJ3GgaJpZM4PGAYH> .

[andrewthad]

Sorry, I corrected my comment on github. I meant to say that we could define a mapMaybeM in vector that is more efficient than witherM specialized to Vector and Maybe.

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Sent from my iPhone

On Aug 29, 2017, at 11:12 PM, Carter Tazio Schonwald ***@***.***> wrote: Sorry... what do you mean by more definition ? On Tue, Aug 29, 2017 at 7:24 PM Andrew Martin ***@***.***> wrote: > I have. Still, the more definition of mapMaybeM would be more efficient > that using witherM. > > — > You are receiving this because you commented. > > > Reply to this email directly, view it on GitHub > <#183 (comment)>, or mute > the thread > <https://github.com/notifications/unsubscribe-auth/AAAQwlQT105_I9lhnIWKte0lVisQYpOwks5sdJ3GgaJpZM4PGAYH> > . > — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub, or mute the thread.

[Shimuuar]

Also witherable instance couldn't be defined for both unboxed and storable vectors

[andrewthad]

I just noticed the absence of these functions again when I was working on something. Is it alright for me to add these to vector?

[cartazio]

Sure. I’m hapoy to help with making sure we have a. Decent stream fusion rep if needed. One question is if a witherable style interface can be supported too?

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On Wed, Apr 4, 2018 at 5:46 PM Andrew Martin ***@***.***> wrote: I just noticed the absence of these functions again when I was working on something. Is it alright for me to add these to vector? — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#183 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAAQwkvnM-Gxaqc6vA5j4Fhc7HDSBCxgks5tlT9NgaJpZM4PGAYH> .

[andrewthad]

What do you mean by a witherable-style interface? Currently, wither is defined as:

wither :: Applicative f => (a -> f (Maybe b)) -> t a -> f (t b)

What I'm proposing is:

mapMaybeM :: Monad m => (a -> m (Maybe b)) -> Vector a -> m (Vector b)

My constraint is stronger, but my understanding is that vector's stream fusion only works with a Monad constraint. So, I don't think that the witherable interface can be supported.