Core Language

Error Handling

try / catch — no exception hierarchy, every caught error is just a message string.

New to coding?

Copy the examples exactly first. Run them. Then change one number or word and run them again. You are not expected to memorize the command lists.

try / catch

The catch variable is optional.

Try this code

try {
    n = to_num("not a number");
} catch err {
    print "failed: {err}";
}

try { risky(); } catch { }   // swallow silently

Throws a catchable error when the condition is falsy — the standard way to signal failure.

Try this code

fn withdraw(balance, amount) {
    assert(amount <= balance, "insufficient funds");
    return balance - amount;
}

Runtime errors point at the exact source location and suggest fixes for typos.

Try this code

print greeet("World");
       ^^^^^^
mko: error (line 4): function 'greeet' wasn't found
  hint: did you mean 'greet'?