9 Conditionals

The if expression allows evaluating different expressions based on a condition.

let a = 42 in if (a % 2 == 0) print("Even") else print("odd");

Since if is itself an expression, returning the value of the branch that evaluated true, the previous program can be rewritten as follows:

let a = 42 in print(if (a % 2 == 0) "even" else "odd");

Conditions are just expressions of boolean type. The following are the valid boolean expressions:

Boolean literals: true and false.
Arithmetic comparison operators: <, >, <=, >=, ==, !=, with their usual semantics.
Boolean operators: & (and), | (or), and ! (not) with their usual semantics.

9.1 Expression blocks in conditionals

The body of the if or the else part of a conditional (or both) can be an expression block as well:

let a = 42 in
    if (a % 2 == 0) {
        print(a);
        print("Even");
    }
    else print("Odd");

The if expression supports multiple branches with the elif construction, which introduces another conditioned branch:

let a = 42, let mod = a % 3 in
    print(
        if (mod == 0) "Magic"
        elif (mod % 3 == 1) "Woke"
        else "Dumb"
    );