Re: [Haskell-cafe] list comprehension doesn't work

Isn't the product check actually redundant? re-reading the requirements we could just define a = 1 and b = x. Maybe I'm misunderstanding though. On Tue, May 14, 2013 at 10:24 AM, Daniel Díaz Casanueva < dhelta.diaz@gmail.com> wrote:

Well, definitely, isSqrt should be called isSquare.

On Tue, May 14, 2013 at 5:22 PM, Daniel Díaz Casanueva < dhelta.diaz@gmail.com> wrote:

...

You can always write it like this:

listPairs = [ (x,y) | x <- [6 .. 499] , y <- [0 .. 1000] , isProduct x , isSqrt y , mod y x == 0 ]

So you have the bounds for x and y, and then the conditions. You then need to define isProduct and isSqrt with types

isProduct :: Int -> Bool isSqrt :: Int -> Bool

Hopefully, these problems will look easier separately.

Well, it's just an idea.

Good luck, Daniel Díaz.

On Tue, May 14, 2013 at 4:57 PM, John wrote:

...

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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