Common Pitfalls

Using the wrong operator

In OCaml, there are different arithmetic operators for floats and integers. Additionally, these operators can only be used on 2 floats or 2 integers. Here are invalid expressions in OCaml

1.0 + 2.0
1 + 2.0
1 +. 2
1 +. 2.0

The correct expression for each of these respectively are

1. +. 2.
float_of_int 1 +. 2.
1 + 2
float_of_int 1 +. 2.

There is no automatic casting of integers to floats or vice-versa in OCaml. Everything is explicit. Here is a list of the integer and float operators

Forgetting parentheses around function arguments

A common mistake is to forget surrounding compound function arguments with parentheses, leading to type errors.

# string_of_int 1+1;;

Error: This expression has type string but an expression was expected of type int

This is because of the precedence. In fact, the above evaluates to

# (string_of_int 1) + 1;;

which is wrong. A correct syntax would be

# string_of_int (1+1);;

- : string = "2"