rust/src/libstd/list.rs

/*
Module: list

A standard linked list
*/

import core::option;
import option::*;
import option::{some, none};

/* Section: Types */

/*
Tag: list
*/
enum 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: copy>(v: [const T]) -> list<T> {
    *vec::foldr(v, @nil::<T>, { |h, t| @cons(h, t) })
}

/*
Function: foldl

Left fold

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

Parameters:

ls - The list to fold
z - The initial value
f - The function to apply
*/
fn foldl<T: copy, U>(ls: list<U>, z: T, f: fn(T, U) -> T) -> T {
    let accum: T = z;
    iter(ls) {|elt| accum = f(accum, elt);}
    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: copy, U: copy>(ls: list<T>, f: fn(T) -> option<U>)
    -> option<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: copy>(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: is_empty

Returns true if the list is empty.
*/
pure fn is_empty<T: copy>(ls: list<T>) -> bool {
    alt ls {
        nil { true }
        _ { false }
    }
}

/*
Function: is_not_empty

Returns true if the list is not empty.
*/
pure fn is_not_empty<T: copy>(ls: list<T>) -> bool {
    ret !is_empty(ls);
}

/*
Function: len

Returns the length of a list
*/
fn len<T>(ls: list<T>) -> uint {
    let count = 0u;
    iter(ls) {|_e| count += 1u;}
    count
}

/*
Function: tail

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

/*
Function: head

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

/*
Function: append

Appends one list to another
*/
pure fn append<T: copy>(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); }
    }
}

/*
Function: iter

Iterate over a list
*/
fn iter<T>(l: list<T>, f: fn(T)) {
    alt l {
      cons(hd, tl) {
        f(hd);
        let cur = tl;
        while true {
            alt *cur {
              cons(hd, tl) {
                f(hd);
                cur = tl;
              }
              nil { break; }
            }
        }
      }
      nil {}
    }
}

#[cfg(test)]
mod tests {

    #[test]
    fn test_is_empty() {
        let empty : list::list<int> = from_vec([]);
        let full1 = from_vec([1]);
        let full2 = from_vec(['r', 'u']);

        assert is_empty(empty);
        assert !is_empty(full1);
        assert !is_empty(full2);

        assert !is_not_empty(empty);
        assert is_not_empty(full1);
        assert is_not_empty(full2);
    }

    #[test]
    fn test_from_vec() {
        let l = from_vec([0, 1, 2]);

        check is_not_empty(l);
        assert (head(l) == 0);

        let tail_l = tail(l);
        check is_not_empty(tail_l);
        assert (head(tail_l) == 1);

        let tail_tail_l = tail(tail_l);
        check is_not_empty(tail_tail_l);
        assert (head(tail_tail_l) == 2);
    }

    #[test]
    fn test_from_vec_empty() {
        let empty : list::list<int> = from_vec([]);
        assert (empty == list::nil::<int>);
    }

    #[test]
    fn test_from_vec_mut() {
        let l = from_vec([mutable 0, 1, 2]);

        check is_not_empty(l);
        assert (head(l) == 0);

        let tail_l = tail(l);
        check is_not_empty(tail_l);
        assert (head(tail_l) == 1);

        let tail_tail_l = tail(tail_l);
        check is_not_empty(tail_tail_l);
        assert (head(tail_tail_l) == 2);
    }

    #[test]
    fn test_foldl() {
        fn add(&&a: uint, &&b: int) -> uint { ret a + (b as uint); }
        let l = from_vec([0, 1, 2, 3, 4]);
        let empty = list::nil::<int>;
        assert (list::foldl(l, 0u, add) == 10u);
        assert (list::foldl(empty, 0u, add) == 0u);
    }

    #[test]
    fn test_foldl2() {
        fn sub(&&a: int, &&b: int) -> int {
            a - b
        }
        let l = from_vec([1, 2, 3, 4]);
        assert (list::foldl(l, 0, sub) == -10);
    }

    #[test]
    fn test_find_success() {
        fn match(&&i: int) -> option<int> {
            ret if i == 2 { option::some(i) } else { option::none::<int> };
        }
        let l = from_vec([0, 1, 2]);
        assert (list::find(l, match) == option::some(2));
    }

    #[test]
    fn test_find_fail() {
        fn match(&&_i: int) -> option<int> { ret option::none::<int>; }
        let l = from_vec([0, 1, 2]);
        let empty = list::nil::<int>;
        assert (list::find(l, match) == option::none::<int>);
        assert (list::find(empty, match) == option::none::<int>);
    }

    #[test]
    fn test_has() {
        let l = from_vec([5, 8, 6]);
        let empty = list::nil::<int>;
        assert (list::has(l, 5));
        assert (!list::has(l, 7));
        assert (list::has(l, 8));
        assert (!list::has(empty, 5));
    }

    #[test]
    fn test_len() {
        let l = from_vec([0, 1, 2]);
        let empty = list::nil::<int>;
        assert (list::len(l) == 3u);
        assert (list::len(empty) == 0u);
    }

}

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