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Control flow and pattern matching

This page covers statements and control-flow forms.

Return​

Canonical return:

return value
return

Explicit return remains the canonical style even where the parser may accept expression-tail bodies in some compatibility paths.

If / elif / else​

Accepted forms:

if ready {
    return 1
}

if ready {
    return 1
} elif waiting {
    return 2
} else {
    return 3
}

While loops​

while x < 10 {
    x += 1
}

For-in loops​

for item in items {
    print(item)
}

The current parsed form is for <name> in <expr> { ... }.

Nested blocks​

Standard blocks are statements:

{
    let x = 1
    print(x)
}

Match as control-oriented expression​

While match is an expression, it often carries control flow:

fn render(value) {
    return match value {
        true => "yes",
        false => "no",
    }
}

Spawn​

Spawn is a statement form, not a function call:

spawn work()
spawn { let x = 1 }

Both forms are supported:

  • spawn an expression
  • spawn a block

See also Concurrency and channels.