rust/src/lib/list.rs

/*
Module: list

A standard linked list
*/

import option::{some, none};

/* Section: Types */

/*
Tag: list
*/
tag list<T> {
    /* Variant: cons */
    cons(T, @list<T>);
    /* Variant: nil */
    nil;
}

/*Section: Operations */

/*
Function: from_vec

Create a list from a vector
*/
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;
}

/*
Function: foldl

Left fold

Applies `f` to the first argument in the list and `u`, then applies
`f` to the second argument and the result of the previous call,
and so on, returning the accumulated result.

Parameters:

ls_ - The list to fold
u - The initial value
f - The function to apply
*/
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;
}

/*
Function: find

Search for an element that matches a given predicate

Apply function `f` to each element of `v`, starting from the first.
When function `f` returns true then an option containing the element
is returned. If `f` matches no elements then none is returned.
*/
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;
}

/*
Function: has

Returns true if a list contains an element with the given value
*/
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;
}

/*
Function: length

Returns the length of a list
*/
fn length<T>(ls: list<T>) -> uint {
    fn count<T>(_t: T, &&u: uint) -> uint { ret u + 1u; }
    ret foldl(ls, 0u, bind count(_, _));
}

/*
Function: cdr

Returns all but the first element of a list
*/
fn cdr<T>(ls: list<T>) -> list<T> {
    alt ls { cons(_, tl) { ret *tl; } nil. { fail "list empty" } }
}

/*
Function: car

Returns the first element of a list
*/
fn car<T>(ls: list<T>) -> T {
    alt ls { cons(hd, _) { ret hd; } nil. { fail "list empty" } }
}

/*
Function: append

Appends one list to another
*/
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: