Calculation on large numbers return 0

[rvdalen]

Hi everyone,

I have the following function definition.

factorial :: Int -> Int

factorial n = go n 1 1

 where

   go :: Int -> Int -> Int -> Int

   go n i r =

     if i == n

       then i * r

       else go n (i + 1) (i * r)

If I apply the `factorial` function to the value `999999999`, it returns 0, which is unexpected.
If I use a smaller number, say `5` it returns 120.

Can someone explain this behavior please?

Regards
--Rouan

[Phil Freeman]

You could try using a library like purescript-hugenums which supports larger integers.

Thanks,

Phil.

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[rvdalen]

Hi Phil,

Thanks for the tip about the purescript-hugenums library.  I will look into that.

What I am more interested at the moment is how to explain the behavior.
Why is this happening? 
What are the limits of `Int` and when can I expect this behavior to kick in? 
Is this documented somewhere?

Regards
--Rouan

[Michael Ficarra]

See https://pursuit.purescript.org/builtins/docs/Prim#t:Int