import option::{some, none};

tag list<T> { cons(T, @list<T>); nil; }

fn from_vec<@T>(v: [T]) -> list<T> {
    let l = nil::<T>;
    // FIXME: This would be faster and more space efficient if it looped over
    // a reverse vector iterator. Unfortunately generic iterators seem not to
    // work yet.

    for item: T in vec::reversed(v) { l = cons::<T>(item, @l); }
    ret l;
}

fn foldl<@T, @U>(ls_: list<T>, u: U, f: block(T, U) -> U) -> U {
    let accum: U = u;
    let ls = ls_;
    while true {
        alt ls {
          cons(hd, tl) { accum = f(hd, accum); ls = *tl; }
          nil. { break; }
        }
    }
    ret accum;
}

fn find<@T, @U>(ls_: list<T>, f: block(T) -> option::t<U>) -> option::t<U> {
    let ls = ls_;
    while true {
        alt ls {
          cons(hd, tl) {
            alt f(hd) { none. { ls = *tl; } some(rs) { ret some(rs); } }
          }
          nil. { break; }
        }
    }
    ret none;
}

fn has<@T>(ls_: list<T>, elt: T) -> bool {
    let ls = ls_;
    while true {
        alt ls {
          cons(hd, tl) { if elt == hd { ret true; } else { ls = *tl; } }
          nil. { break; }
        }
    }
    ret false;
}

fn length<@T>(ls: list<T>) -> uint {
    fn count<T>(_t: T, &&u: uint) -> uint { ret u + 1u; }
    ret foldl(ls, 0u, count);
}

fn cdr<@T>(ls: list<T>) -> list<T> {
    alt ls { cons(_, tl) { ret *tl; } nil. { fail "list empty" } }
}

fn car<@T>(ls: list<T>) -> T {
    alt ls { cons(hd, _) { ret hd; } nil. { fail "list empty" } }
}

fn append<@T>(l: list<T>, m: list<T>) -> list<T> {
    alt l {
      nil. { ret m; }
      cons(x, xs) { let rest = append(*xs, m); ret cons(x, @rest); }
    }
}

// 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: