Pattern Matching

Pattern matching is a mechanism for checking a value against a pattern.

Syntax#

A match expression has a value, the match keyword, and at least one case clause.

const data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
const result = binarySearch(data, 3);
match result {
    case Some(_) => print("1: found")
    case None => print("1: not found")
}

Match Literal Value#

Match expressions have a value.

function myNot(v: boolean): boolean {
    match v {
        case true => false
        case false => true
    }
}

function isSix(num: i32): boolean {
    match num {
        case 6 => true
        case _ => false
    }
}

Match Enumerations#

let a = Some(1);
match a {
    case Some(i) => {
        print("Some")
    }
    case None => {
        print("None")
    }
}

Match Arrays#

Match an array with fixed length:

function isOneTwoThree(arr: i32[]): boolean {
    match arr {
        case [1,2,3] => true
        case _ => false
    }
}

Match an array with unlimited length:

function isOneTwoThreeMore(arr: i32[]): boolean {
    match arr {
        case [1,2,3, ..._] => true
        case _ => false
    }
}

Binding variable to pattern:

function printRest(arr: i32[]) {
    match arr {
        case [1,2,3, ...rest] => print(rest)
        case _ => {}
    }
}