[Haskell-cafe] list comprehension doesn't work

[Alejandro Serrano Mena]

For a first sight, you cannot use x <- [0..]*[0..] to mean 'all possible
pairs x = a*b'.
You would need to do something like
[ (a*b, y) | a <- [0..], b <- [0..], a*b > 5, a*b < 500, and the rest of
things ]


2013/5/14 John <knowledge1202 at gmail.com>

> Hi,
>
> I have to write a function which returns a list of all pairs (x,y) where x,
> y ∈ N AND:
> –  x is the product of two natural numbers (x = a · b, where a, b ∈ N) AND
> –  x is really bigger than 5 but really smaller than 500, AND
> –  y is a squer number (y = c² where c ∈ N) NOT greater than 1000, AND
> –  x is a divisor of y.
>
> My attempt is as follows:
>
> listPairs :: [(Int, Int)]
> listPairs = [(x,y) | x<-[0..], y<-[0..], x<-[0..]*[0..], x > 5, x < 500,
> (y*y) < 1001, mod y x == 0]
>
> However it doesn't work unfortunatly
>
> Could anyone tell me where my mistake is?
>
> Thanks.
>
>
>
> --
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