1		% (c) 2009-2026 Lehrstuhl fuer Softwaretechnik und Programmiersprachen,
2		% Heinrich Heine Universitaet Duesseldorf
3		% This software is licenced under EPL 1.0 (http://www.eclipse.org/org/documents/epl-v10.html)
4
5		:- module(gensym,
6		[gensym/2, get_gensym_counter/2,
7		reset_gensym/0,
8		gennum/1, gennum_count/1, reset_gennum/0, reset_gennum/1]).
9
10		:- use_module(module_information).
11		:- module_info(group,tools).
12		:- module_info(description,'Tools for generating fresh symbols and numbers.').
13
14		:- use_module(tools_strings, [string_concatenate/3]).
15
16		/* ===================================================== */
17
18		/* ------ */
19		/* GENSYM */
20		/* ------ */
21
22		/* generate a new symbol with the given prefix */
23		/* code from the "Art of Prolog" */
24		gensym(Prefix,V) :-
25		var(V),
26		atom(Prefix),
27		oldvalue(Prefix,N),
28		N1 is N + 1,
29		set_flag(Prefix,N1),
30		string_concatenate(Prefix,'__',PreSep),
31		string_concatenate(PreSep,N1,V).
32		get_gensym_counter(Prefix,R) :- (flag(Prefix,Count) -> R=Count ; R=0).
33
34		:- dynamic gennum_count/1.
35		gennum_count(0).
36
37		gennum(Nr) :-
38		retract(gennum_count(Nr)), N1 is Nr + 1,
39		assertz(gennum_count(N1)).
40
41		reset_gensym :- retractall(flag(_,_)).
42		reset_gennum :- reset_gennum(0).
43
44		reset_gennum(Nr) :- retractall(gennum_count(_)), assertz(gennum_count(Nr)).
45
46		oldvalue(Prefix,N) :- flag(Prefix,N),!.
47		oldvalue(_Prefix,0).
48		set_flag(Name,X) :-
49		nonvar(Name),
50		retract(flag(Name,_Val)),!,
51		asserta(flag(Name,X)).
52		set_flag(Name,X) :-
53		nonvar(Name),
54		asserta(flag(Name,X)).
55
56		:- dynamic flag/2.
57		%flag(foo,foo) :- fail.
58