[Haskell-beginners] strange behaviour : computing lowest divisor

[Lyndon Maydwell]

Try with Integer rather than Int. Might be an overflow issue...

On Wed, Dec 29, 2010 at 5:32 PM, Abhijit Ray <avizit at gmail.com> wrote:
> HI,
> I have written(copied) a small piece of code which finds the lowest divisor
> of am integer (greater than 1)
>
> the code is here
>
> ld::Int->Int
> ld n = ld' 2 n
>        where
>   ld' i n | rem n i == 0 = i
>                  | i^2 > n = n
>                  | otherwise = ld' (i+1) n
>
>
> now it seems to work fine for small numbers but for a big number we get
>
> *Main> ld 278970415063349480483707695
> 7
>
> the number is obviously divisible by 5 , so where is the anomaly ?
>
> Thanks,
> Abhijit
> On Wed, Dec 29, 2010 at 2:52 PM, Alex Rozenshteyn <rpglover64 at gmail.com>
> wrote:
>>
>> I'm trying to understand the technique referred to as "tying the knot",
>> but documentation on the internet seems to be much sparser and more obtuse
>> than I like.
>>
>> So I'm asking here.
>>
>> As far as I understand, "tying the knot" refers to a way of using laziness
>> to implement something like references in a purely functional way.
>>
>> I'm trying to write a toy simulation:
>> I have a population :: [Person]
>> I want to collect a random subset of possible pairs of distinct people.
>> So I go to each person in the population and select a subset of the people
>> after him/her in the list; these are pairs in which s/he is the first
>> element.
>>
>> I want to then be able to ask for all pairs in which a person is the first
>> or the second element.  I could give each person a unique id, but it seems
>> like tying the knot is a valid way to implement this.
>>
>> Please correct me if I am misunderstanding.
>>
>> Thank you.
>>
>> --
>>           Alex R
>>
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>
>
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