[Haskell-cafe] Parse text difficulty

Jan-Willem Maessen - Sun Labs East Janwillem.Maessen at Sun.COM
Thu Dec 9 11:46:39 EST 2004

Tomasz Zielonka wrote:
> On Thu, Dec 09, 2004 at 10:02:39AM -0500, Jan-Willem Maessen - Sun Labs East wrote:
>>And I thought that most programmers used "zipWith", which has to be
> You can also use zipWith to simulate zipN, for any N (however, the following
> code uses infix notation):
> Prelude> let l = words "Haskell is great"
> Prelude> let zwApply = zipWith ($)
> Prelude> repeat (,,) `zwApply` [1..] `zwApply` l `zwApply` map length l
> [(1,"Haskell",7),(2,"is",2),(3,"great",5)]
> Prelude> map (,,) l `zwApply` [1..] `zwApply` map length l
> [("Haskell",1,7),("is",2,2),("great",3,5)]
> I found it useful recently, when I needed zip functions for Trees - this way I
> didn't have to define functions for 3 trees, 4 trees, and so on.

Note also that:

repeat f `zwApply` xs  =  map f xs

When cooking up my own collection-y things (including splittable
supplies, for example), I generally provide fmap and an equivalent of
zwApply (a generic repeat is not quite so simple or useful).  It's a
nice little idiom, and a recommend it highly.

-Jan-Willem Maessen

> Best regards,
> Tomasz
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