List comprehensions

[Oliver Braun]

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* Rijk J. C. van Haaften <rjchaaft@cs.uu.nl> [2003-01-30 12:06 +0100]:

> >* Rijk J. C. van Haaften <rjchaaft@cs.uu.nl> [2003-01-30 11:41 +0100]:
> >
> >> Recently, I came accross this expression:
> >> [ x + y | x <- xs | y <- ys ]
> >                    ^
> >                    Put a comma ',' here.

> That's something totally different. Two examples:
> 1. Comma
>   [ x + y | x <- [1,2], y <- [3,4] ]
> =3D [4,5,5,6]

> 2. Bar
>   [ x + y | x <- [1,2] | y <- [3,4] ]
> =3D [ x + y | (x,y) <- zip [1,2] [3,4] ]
> =3D zipWith (+) [1,2] [3,4]
> =3D [4,6]

> The first is according to the standard. No problems so far.
> However, I couldn't find a description of the semantics of
> the second (and it is clearly non-standard), though I think
> the semantics given above using zip and zipWith are correct.

Ok, I see. Sorry, this was just my first thought.
Unfortunately I cannot help you with the Bar thing.

Regards,
         Olli
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