On 26 Aug 2010, at 08:01, michael rice wrote:
> Hmm... it was my understanding that the example was showing how to *avoid*
> having to create a lot of functions that do the same thing but have
> different numbers of arguments.
>
> From the Wiki page:
>
> "Anytime you feel the need to define different higher order functions to
> accommodate for function-arguments with a different number of arguments,
> think about how defining a proper instance of Applicative can make your life
> easier."
>
> Not so?
>
>
Very much so – instead of defining liftA2, liftA3 etc like this, just use pure
to get things into the applicative, and write <*> instead of ' ' to apply
applicatives and you're done.
Don't write
liftA3 sumsq (Just 3) (Just 4) (Just 5)
Write
(pure sumsq) <*> (pure 3) <*> (pure 4) <*> (pure 5)
or you can get rid of that first pure with a quick fmap:
sumsq <$> (pure 3) <*> (pure 4) <*> (pure 5)
Bob
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