rust/src/lib/either.rs

import option;
import option::some;
import option::none;

tag t[T, U] { left(T); right(U); }

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

fn either[T, U,
          V](f_left: &operator[T, V], f_right: &operator[U, V],
             value: &t[T, U]) -> V {
    alt value { left(l) { f_left(l) } right(r) { f_right(r) } }
}

fn lefts[T, U](eithers: &(t[T, U])[]) -> T[] {
    let result: T[] = ~[];
    for elt: t[T, U]  in eithers {
        alt elt { left(l) { result += ~[l] } _ {/* fallthrough */ } }
    }
    ret result;
}

fn rights[T, U](eithers: &(t[T, U])[]) -> U[] {
    let result: U[] = ~[];
    for elt: t[T, U]  in eithers {
        alt elt { right(r) { result += ~[r] } _ {/* fallthrough */ } }
    }
    ret result;
}

fn partition[T, U](eithers: &(t[T, U])[]) -> {lefts: T[], rights: U[]} {
    let lefts: T[] = ~[];
    let rights: U[] = ~[];
    for elt: t[T, U]  in eithers {
        alt elt { left(l) { lefts += ~[l] } right(r) { rights += ~[r] } }
    }
    ret {lefts: lefts, rights: rights};
}
//
// 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 $RBUILD 2>&1 | sed -e 's/\\/x\\//x:\\//g'";
// End:
//