Operators as Functions

The addition operator + has type int->int->int. It is normally written infix, e.g., 3 + 4. By putting parentheses around it, we can make it a prefix operator:

# (+);;
- : int -> int -> int = <fun>

# (+) 3 4;;
- : int = 7

# let add3 = (+) 3;;
- : int -> int = <fun>

# add3 2;;
- : int = 5

The same technique works for any built-in operator. But be careful of multiplication, which must be written ( * ) as prefix, because (*) would be parsed as beginning a comment.

We can even define our own new infix operators, for example:

let (^^) x y = max x y

And now 2 ^^ 3 evaluates to 3. The rules for which punctuation can be used to create infix operators, and the relative precedence that operator will have, are not necessarily intuitive. So be careful with this usage.