Editing OCaml (section)

===Arbitrary-precision factorial function (libraries)===
A variety of libraries are directly accessible from OCaml. For example, OCaml has a built-in library for [[arbitrary-precision arithmetic]]. As the factorial function grows very rapidly, it quickly overflows machine-precision numbers (typically 32- or 64-bits). Thus, factorial is a suitable candidate for arbitrary-precision arithmetic.

In OCaml, the Num module (now superseded by the ZArith module) provides arbitrary-precision arithmetic and can be loaded into a running top-level using:
<syntaxhighlight lang=ocaml>
# #use "topfind";;
# #require "num";;
# open Num;;
</syntaxhighlight>

The factorial function may then be written using the arbitrary-precision numeric operators {{mono|{{=}}/}}, {{mono|*/}} and {{mono|-/}} :

<syntaxhighlight lang="OCaml">
# let rec fact n =
    if n =/ Int 0 then Int 1 else n */ fact(n -/ Int 1);;
val fact : Num.num -> Num.num = <fun>
</syntaxhighlight>

This function can compute much larger factorials, such as 120!:

<syntaxhighlight lang="OCaml">
# string_of_num (fact (Int 120));;
- : string =
"6689502913449127057588118054090372586752746333138029810295671352301633
55724496298936687416527198498130815763789321409055253440858940812185989
8481114389650005964960521256960000000000000000000000000000"
</syntaxhighlight>