-- Copyright 1993-1998, by the Cecil Project
-- Department of Computer Science and Engineering, University of Washington
-- See the LICENSE file for license information.

(--DOC
  A `sequence' is an ordered collection where the ordering of the elements is
  determined externally, by the way they were put into the collection. (In
  contrast, a sorted collection is an ordered collection where the order is
  determined by the elements themselves and the `<' binary ordering predicate
  over the elements.)
--)

abstract object sequence[T] isa ordered_collection[T];
extend type sequence[`T] subtypes sequence[`S >= T];

--DOC Concatenating two sequences always produces a new sequence
method ||(s1@:sequence[`T], s2@:sequence[`T]):sequence[T] {
    let var new:simple_list[T] := nil[T];
    reverse_do(s2, &(e:T){ new := cons(e, new); });
    reverse_do(s1, &(e:T){ new := cons(e, new); });
    new }

precedence || left_associative above =;


signature copy(sequence[`T]):sequence[T];