rust/src/lib/option.rs

// lib/option::rs

tag t[T] {
    none;
    some(T);
}

type operator[T, U] = fn(&T) -> U;

fn get[T](&t[T] opt) -> T {
    ret alt (opt) {
        case (some(?x)) {
            x
        }
        case (none) {
            fail
        }
    };
}

fn map[T, U](&operator[T, U] f, &t[T] opt) -> t[U] {
    ret alt (opt) {
        case (some(?x)) {
            some[U](f(x))
        }
        case (none) {
            none[U]
        }
    };
}

fn is_none[T](&t[T] opt) -> bool {
    ret alt (opt) {
        case (none)      { true }
        case (some(_))   { false }
    };
}

fn from_maybe[T](&T def, &t[T] opt) -> T {
    auto f = bind util::id[T](_);
    ret maybe[T, T](def, f, opt);
}

fn maybe[T, U](&U def, fn(&T) -> U f, &t[T] opt) -> U {
    ret alt (opt) {
        case (none) { def }
        case (some(?t)) { f(t) }
    };
}

// Can be defined in terms of the above when/if we have const bind.
fn may[T](fn(&T) f, &t[T] opt) {
    alt (opt) {
        case (none) { /* nothing */ }
        case (some(?t)) { f(t); }
    }
}

// Local Variables:
// mode: rust;
// fill-column: 78;
// indent-tabs-mode: nil
// c-basic-offset: 4
// buffer-file-coding-system: utf-8-unix
// compile-command: "make -k -C .. 2>&1 | sed -e 's/\\/x\\//x:\\//g'";
// End: