# [Haskell-cafe] How to decide if a number is an integer?

Magicloud Magiclouds magicloud.magiclouds at gmail.com
Tue Sep 29 04:30:50 EDT 2009

```Resolved. As Thomas said, mixing up sure is a bad thing. But then I
have to name so many meanless (at least I think) computing process....

On Tue, Sep 29, 2009 at 3:32 PM, Jimmy Hartzell <jim at shareyourgifts.net> wrote:
> *Should* isInteger be returning True for any numbers generated by this
> code?  If so, can you simplify this test down to that example, so that
> it's obvious what the test should do, and that it's not doing it (if it in
> fact is not doing as it should)? In any case, it would help to divide this
> block of code into more manageable pieces.
>
> isInteger should have the type Fractional a => a -> Boolean.
>
>> The properFaction part is correct. So I posted the whole code, since
>> "isInteger" should accept any reasonable incoming types. Well, in this
>> one situation, it does not. And I cannot figure out why....
>>
>> On Tue, Sep 29, 2009 at 3:07 PM, Jimmy Hartzell <jim at shareyourgifts.net>
>> wrote:
>>> Did you test the properFraction-based code in isolation? If code is
>>> broken, it's important to figure out which part of it is broken. Also,
>>> this function is not divided into constituent parts, but is a long
>>> unruly
>>> mess. Dividing it into parts would make it much much more readable, and
>>> you would then be able to test the parts individually.
>>>
>>> Jimmy
>>>
>>>> The original code is
>>>> givenSum num = map (\a ->
>>>>                       let l = (sqrt \$ fromIntegral (a * a +
>>>> 2 + 2 *
>>>> num)) - (fromIntegral a) in
>>>>                       case properFraction l of
>>>>                         (_, 0) ->
>>>>                           True
>>>>                         _ ->
>>>>                           False
>>>>                    ) \$ take num [1..]
>>>> :t l is (Floating a) => a
>>>> Well, in ghci
>>>> *Main> givenSum 10
>>>> [False,False,False,False,False,False,False,False,False,False]
>>>>
>>>> On Tue, Sep 29, 2009 at 2:45 PM, Thomas DuBuisson
>>>> <thomas.dubuisson at gmail.com> wrote:
>>>>> On Mon, Sep 28, 2009 at 11:35 PM, Magicloud Magiclouds
>>>>> <magicloud.magiclouds at gmail.com> wrote:
>>>>>> It never matches to (_, 0.0)....
>>>>>> I mean
>>>>>> case properFraction l of
>>>>>>  (_, 0) -> l
>>>>>>  _ -> 0 -- always goes here.
>>>>>
>>>>> Odd, it works fine for me.
>>>>>
>>>>> f x =
>>>>>        case properFraction x of
>>>>>                (_,0) -> True
>>>>>                _     -> False
>>>>>
>>>>>
>>>>> *Main> f 5
>>>>> True
>>>>> *Main> f 5.5
>>>>> False
>>>>> *Main> f 4.0
>>>>> True
>>>>> *Main> f 4.00000001
>>>>> False
>>>>>
>>>>>
>>>>> Thomas
>>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> 竹密岂妨流水过
>>>> 山高哪阻野云飞
>>>>
>>>
>>>
>>>
>>
>>
>>
>> --
>> 竹密岂妨流水过
>> 山高哪阻野云飞
>>
>
>
>

--

```