mirror of
https://github.com/KevinMidboe/linguist.git
synced 2025-10-29 17:50:22 +00:00
281 lines
7.0 KiB
Prolog
281 lines
7.0 KiB
Prolog
% This file has been included as an YAP library by Vitor Santos Costa, 1999
|
|
|
|
% File : QUEUES.PL
|
|
% Author : R.A.O'Keefe
|
|
% Updated: Friday November 18th, 1983, 8:09:31 pm
|
|
% Purpose: define queue operations
|
|
% Needs : lib(lists) for append/3.
|
|
|
|
/** @defgroup Queues Queues
|
|
@ingroup library
|
|
@{
|
|
|
|
The following queue manipulation routines are available once
|
|
included with the `use_module(library(queues))` command. Queues are
|
|
implemented with difference lists.
|
|
|
|
*/
|
|
|
|
/**
|
|
|
|
@pred make_queue(+ _Queue_)
|
|
|
|
|
|
Creates a new empty queue. It should only be used to create a new queue.
|
|
|
|
|
|
*/
|
|
|
|
|
|
/** @pred empty_queue(+ _Queue_)
|
|
|
|
|
|
Tests whether the queue is empty.
|
|
|
|
|
|
*/
|
|
/** @pred head_queue(+ _Queue_, ? _Head_)
|
|
|
|
|
|
Unifies Head with the first element of the queue.
|
|
|
|
|
|
*/
|
|
/** @pred join_queue(+ _Element_, + _OldQueue_, - _NewQueue_)
|
|
|
|
|
|
Adds the new element at the end of the queue.
|
|
|
|
|
|
*/
|
|
/** @pred jump_queue(+ _Element_, + _OldQueue_, - _NewQueue_)
|
|
|
|
|
|
Adds the new element at the front of the list.
|
|
|
|
|
|
*/
|
|
/** @pred length_queue(+ _Queue_, - _Length_)
|
|
|
|
|
|
Counts the number of elements currently in the queue.
|
|
|
|
|
|
*/
|
|
/** @pred list_join_queue(+ _List_, + _OldQueue_, - _NewQueue_)
|
|
|
|
|
|
Ads the new elements at the end of the queue.
|
|
|
|
|
|
*/
|
|
/** @pred list_jump_queue(+ _List_, + _OldQueue_, + _NewQueue_)
|
|
|
|
|
|
Adds all the elements of _List_ at the front of the queue.
|
|
|
|
|
|
*/
|
|
/** @pred list_to_queue(+ _List_, - _Queue_)
|
|
|
|
|
|
Creates a new queue with the same elements as _List._
|
|
|
|
|
|
*/
|
|
/** @pred queue_to_list(+ _Queue_, - _List_)
|
|
|
|
|
|
Creates a new list with the same elements as _Queue_.
|
|
|
|
|
|
|
|
|
|
*/
|
|
/** @pred serve_queue(+ _OldQueue_, + _Head_, - _NewQueue_)
|
|
|
|
|
|
Removes the first element of the queue for service.
|
|
|
|
|
|
*/
|
|
:- module(queues, [
|
|
make_queue/1, % create empty queue
|
|
join_queue/3, % add element to end of queue
|
|
list_join_queue/3, % add many elements to end of queue
|
|
jump_queue/3, % add element to front of queue
|
|
list_jump_queue/3, % add many elements to front of queue
|
|
head_queue/2, % look at first element of queue
|
|
serve_queue/3, % remove first element of queue
|
|
length_queue/2, % count elements of queue
|
|
empty_queue/1, % test whether queue is empty
|
|
list_to_queue/2, % convert list to queue
|
|
queue_to_list/2 % convert queue to list
|
|
]).
|
|
|
|
:- use_module(library(lists), [append/3]).
|
|
|
|
/*
|
|
:- mode
|
|
make_queue(-),
|
|
join_queue(+, +, -),
|
|
list_join_queue(+, +, -),
|
|
jump_queue(+, +, -),
|
|
list_jump_queue(+, +, -),
|
|
head_queue(+, ?),
|
|
serve_queue(+, ?, -),
|
|
length_queue(+, ?),
|
|
length_queue(+, +, +, -),
|
|
empty_queue(+),
|
|
list_to_queue(+, -),
|
|
queue_to_list(+, -),
|
|
queue_to_list(+, +, -).
|
|
*/
|
|
|
|
/* In this package, a queue is represented as a term Front-Back, where
|
|
Front is a list and Back is a tail of that list, and is normally a
|
|
variable. join_queue will only work when the Back is a variable,
|
|
the other routines will accept any tail. The elements of the queue
|
|
are the list difference, that is, all the elements starting at Front
|
|
and stopping at Back. Examples:
|
|
|
|
[a,b,c,d,e|Z]-Z has elements a,b,c,d,e
|
|
[a,b,c,d,e]-[d,e] has elements a,b,c
|
|
Z-Z has no elements
|
|
[1,2,3]-[1,2,3] has no elements
|
|
*/
|
|
|
|
% make_queue(Queue)
|
|
% creates a new empty queue. It will also match empty queues, but
|
|
% because Prolog doesn't do the occurs check, it will also match
|
|
% other queues, creating circular lists. So this should ONLY be
|
|
% used to make new queues.
|
|
|
|
make_queue(X-X).
|
|
|
|
|
|
|
|
% join_queue(Element, OldQueue, NewQueue)
|
|
% adds the new element at the end of the queue. The old queue is
|
|
% side-effected, so you *can't* do
|
|
% join_queue(1, OldQ, NewQ1),
|
|
% join_queue(2, OldQ, NewQ2).
|
|
% There isn't any easy way of doing that, sensible though it might
|
|
% be. You *can* do
|
|
% join_queue(1, OldQ, MidQ),
|
|
% join_queue(2, MidQ, NewQ).
|
|
% See list_join_queue.
|
|
|
|
join_queue(Element, Front-[Element|Back], Front-Back).
|
|
|
|
|
|
|
|
% list_join_queue(List, OldQueue, NewQueue)
|
|
% adds the new elements at the end of the queue. The elements are
|
|
% added in the same order that they appear in the list, e.g.
|
|
% list_join_queue([y,z], [a,b,c|M]-M, [a,b,c,y,z|N]-N).
|
|
|
|
list_join_queue(List, Front-OldBack, Front-NewBack) :-
|
|
append(List, OldBack, NewBack).
|
|
|
|
|
|
|
|
% jump_queue(Element, OldQueue, NewQueue)
|
|
% adds the new element at the front of the list. Unlike join_queue,
|
|
% jump_queue(1, OldQ, NewQ1),
|
|
% jump_queue(2, OldQ, NewQ2)
|
|
% *does* work, though if you add things at the end of NewQ1 they
|
|
% will also show up in NewQ2. Note that
|
|
% jump_queue(1, OldQ, MidQ),
|
|
% jump_queue(2, MidQ, NewQ)
|
|
% makes NewQ start 2, 1, ...
|
|
|
|
jump_queue(Element, Front-Back, [Element|Front]-Back).
|
|
|
|
|
|
|
|
% list_jump_queue(List, OldQueue, NewQueue)
|
|
% adds all the elements of List at the front of the queue. There are
|
|
% two ways we might do this. We could add all the elements one at a
|
|
% time, so that they would appear at the beginning of the queue in the
|
|
% opposite order to the order they had in the list, or we could add
|
|
% them in one lump, so that they have the same order in the queue as
|
|
% in the list. As you can easily add the elements one at a time if
|
|
% that is what you want, I have chosen the latter.
|
|
|
|
list_jump_queue(List, OldFront-Back, NewFront-Back) :-
|
|
append(List, OldFront, NewFront).
|
|
% reverse(List, OldFront, NewFront). % for the other definition
|
|
|
|
|
|
|
|
% head_queue(Queue, Head)
|
|
% unifies Head with the first element of the queue. The tricky part
|
|
% is that we might be at the end of a queue: Back-Back, with Back a
|
|
% variable, and in that case this predicate should not succeed, as we
|
|
% don't know what that element is or whether it exists yet.
|
|
|
|
head_queue(Front-Back, Head) :-
|
|
Front \== Back, % the queue is not empty
|
|
Front = [Head|_].
|
|
|
|
|
|
|
|
% serve_queue(OldQueue, Head, NewQueue)
|
|
% removes the first element of the queue for service.
|
|
|
|
serve_queue(OldFront-Back, Head, NewFront-Back) :-
|
|
OldFront \== Back,
|
|
OldFront = [Head|NewFront].
|
|
|
|
|
|
|
|
% empty_queue(Queue)
|
|
% tests whether the queue is empty. If the back of a queue were
|
|
% guaranteed to be a variable, we could have
|
|
% empty_queue(Front-Back) :- var(Front).
|
|
% but I don't see why you shouldn't be able to treat difference
|
|
% lists as queues if you want to.
|
|
|
|
empty_queue(Front-Back) :-
|
|
Front == Back.
|
|
|
|
|
|
|
|
% length_queue(Queue, Length)
|
|
% counts the number of elements currently in the queue. Note that
|
|
% we have to be careful in checking for the end of the list, we
|
|
% can't test for [] the way length(List) does.
|
|
|
|
length_queue(Front-Back, Length) :-
|
|
length_queue(Front, Back, 0, N),
|
|
Length = N.
|
|
|
|
length_queue(Front, Back, N, N) :-
|
|
Front == Back, !.
|
|
length_queue([_|Front], Back, K, N) :-
|
|
L is K+1,
|
|
length_queue(Front, Back, L, N).
|
|
|
|
|
|
|
|
% list_to_queue(List, Queue)
|
|
% creates a new queue with the same elements as List.
|
|
|
|
list_to_queue(List, Front-Back) :-
|
|
append(List, Back, Front).
|
|
|
|
|
|
|
|
% queue_to_list(Queue, List)
|
|
% creates a new list with the same elements as Queue.
|
|
|
|
queue_to_list(Front-Back, List) :-
|
|
queue_to_list(Front, Back, List).
|
|
|
|
queue_to_list(Front, Back, Ans) :-
|
|
Front == Back, !, Ans = [].
|
|
queue_to_list([Head|Front], Back, [Head|Tail]) :-
|
|
queue_to_list(Front, Back, Tail).
|
|
|