Recursion

# factorial.esq
fn factorial(n: i32) -> i32 = {
    if n <= 1 { 1 }
    else { n * factorial(n - 1) }
}

fn main() -> i32 = factorial(5)

$ ./esquec build factorial.esq -o fact
$ ./fact; echo $?
120

Notes

• Functions can call themselves; mutual recursion also works because the compiler collects all top-level signatures in a first pass.
• if is an expression: both arms produce i32, so the whole if produces i32.
• The compiler does not yet do tail-call optimisation. Recursive programs that recurse deeper than the stack tolerates will overflow. Use iterate_until or iterate for tight numeric loops.

A second example: GCD

fn gcd(a: i32, b: i32) -> i32 = {
    if b == 0 { a }
    else { gcd(b, a % b) }
}

fn main() -> i32 = gcd(252, 105)   # 21

A textbook Euclidean algorithm. Pattern matching would also work but the if-form reads fine.