[Haskell] LiftA2 over fmap

[Damien BIHEL]

In the documentation here

it's written that for some functors liftA2 has better performance than
fmap. Does anyone have any examples ?

Regards,

-- 
Damien Bihel
R&D (Research & Development) Engineer at ELRA (European Language Resources
Association)
E-Mail: biheldam...@gmail.com
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Re: [Haskell] LiftA2 over fmap

[Edward Kmett]

> In particular, if fmap

 is an expensive operation, it is likely better to use liftA2

 than to (fmap

 over the structure *and then use <*>
)*
. (emphasis and parens added).

Consider any data constructor that has a strict spine and look at

f <$> m <*> n

This has to walk `m` twice. Once for the fmap on the first argument, and
once for the <*>, but the liftA2 version can walk `m` once fusing things
together.

-Edward

On Tue, Jan 30, 2018 at 4:42 AM, Damien BIHEL  wrote:

> In the documentation here
> 
> it's written that for some functors liftA2 has better performance than
> fmap. Does anyone have any examples ?
>
> Regards,
>
> --
> Damien Bihel
> R&D (Research & Development) Engineer at ELRA (European Language Resources
> Association)
> E-Mail: biheldam...@gmail.com
>
> ___
> Haskell mailing list
> Haskell@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell
>
>
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