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Control Flow

mType supports the usual structured control statements plus pattern matching (covered separately).

if / else​

if (x > 0) {
    print("positive");
} else if (x < 0) {
    print("negative");
} else {
    print("zero");
}

Loops​

for​

for (int i = 0; i < 5; i++) {
    print(i);
}

while​

int n = 0;
while (n < 5) {
    n = n + 1;
}

do / while​

int dk = 0;
do {
    dk = dk + 1;
} while (dk < 2);

Enhanced for (for-each)​

Iterate any Iterable<T>:

for (String word : list) {
    print(word);
}

break and continue​

for (int i = 0; i < 10; i++) {
    if (i == 5) { break; }
    if (i % 2 == 0) { continue; }
    print(i);
}

switch / case / default​

int x = 2;
switch (x) {
    case 1:
        print(100);
        break;
    case 2:
        print(200);
        break;
    case 3:
        print(300);
        break;
    default:
        print(999);
        break;
}

break is required to prevent fall-through. For typed dispatch, use Pattern Matching.

try / catch / finally​

import * from "lib/exceptions/Exception.mt";

function test(): int {
    try {
        throw new Exception("Test exception");
    } catch (Exception e) {
        print("In catch: " + e.getMessage());
        return 30;
    } finally {
        print("In finally");
        return 40;  // overrides the catch return
    }
}

A finally block always executes; its return overrides earlier returns from try or catch.

Custom errors subclass Exception (or one of RuntimeException, IllegalArgumentException, IndexOutOfBoundsException, NullPointerException, ClassNotFoundException).

class ValidationException extends Exception {
    public constructor(string message): super(message) { }
}

throw​

if (input == null) {
    throw new IllegalArgumentException("input cannot be null");
}

Methods that throw checked exceptions should declare them with @Throw:

@Throw(exceptions = [ValidationException])
public function validate(string input): bool { ... }

See Also​