[Haskell-cafe] list comprehension doesn't work

[Danny Gratzer]

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 at gmail.com> wrote:

> Well, definitely, isSqrt should be called isSquare.
>
>
> On Tue, May 14, 2013 at 5:22 PM, Daniel Díaz Casanueva <
> dhelta.diaz at 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 <knowledge1202 at gmail.com> 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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>>>
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>>
>>
>>
>> --
>> E-mail sent by Daniel Díaz Casanueva
>>
>> let f x = x in x
>>
>
>
>
> --
> E-mail sent by Daniel Díaz Casanueva
>
> let f x = x in x
>
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-- 
Danny Gratzer
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