[Haskell-cafe] Re: Suggestions for improvement

[N. Raghavendra]

At 2010-10-03T22:45:30+02:00, Dominique Devriese wrote:

> Additionally, you can't combine the functions (blowup . allButLast)
> and lastToTheLength into a function that returns a pair like you seem
> to attempt. You need a function like the following for that:
>
> comma :: (a -> b) -> (a -> c) -> a -> (b,c)
> comma f g x = (f x, g x)
>
> Then you could say:
>
> blowup = (uncurry (++)) . comma (blowup . allButLast) lastToTheLength

Thanks, I'll try that.

> Ignore this if you haven't read about Applicative or type classes yet,
> but using the Applicative instance for arrow types (->) a, you can
> also write
>
> comma = liftA2 (,)

I hadn't come up to that point, but will read about it now.

Regards,
Raghavendra.

-- 
N. Raghavendra <raghu at mri.ernet.in> | http://www.retrotexts.net/
Harish-Chandra Research Institute   | http://www.mri.ernet.in/
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