Question

I tried to write my own fib function that works for large numbers (over 50) and I had no luck. First I tried the obvious solution but that overflows way to quicly. my next solution was this

    $fun fib(a:int, b:int, index:int) = if(index = 1) then
    $                                      (a+b)
    $                                   else
    $                                       fib(b, (a+b), index - 1);

Unfortunatly this also overflows.

Answer 1

You need to take a look at the IntInf module, which provides access to arbitrary precision integers.

You can convert from Int.int to IntInf.int using IntInf.fromInt.

Note, for any operations you do on them, you have to use IntInf.<operation> instead of the Int counterpart. This includes things like addition and the likes.