function with multiple arguments in OCaml

Question

I am trying to write a function to increment a mutable int by a specified amount.

let increase var:int ref amount = (var := !var+amount;var);;

This is what I came up with, but it produces errors. What is the correct way to do it?

Answer 1

Your only problem is in the specification of the type of var. You need to use parentheses:

# let increase (var: int ref) amount = var := !var + amount; var;;
val increase : int ref -> int -> int ref = <fun>

For what it's worth, the type specification is optional. OCaml will infer the type.

(I would personally consider having the function return unit, which would make it analogous to the built-in function incr.)