1		% (c) 2009-2019 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
6
7		:- module(gensym,
8		[gensym/2, get_gensym_counter/2,
9		reset_gensym/0,
10		gennum/1, gennum_count/1, reset_gennum/0, reset_gennum/1]).
11
12		:- use_module(module_information).
13		:- module_info(group,tools).
14		:- module_info(description,'Tools for generating fresh symbols and numbers.').
15
16		:- use_module(tools_strings, [string_concatenate/3]).
17
18		/* ===================================================== */
19
20		/* ------ */
21		/* GENSYM */
22		/* ------ */
23
24		/* generate a new symbol with the given prefix */
25		/* code from the "Art of Prolog" */
26		gensym(Prefix,V) :-
27		var(V),
28		atom(Prefix),
29		oldvalue(Prefix,N),
30		N1 is N + 1,
31		set_flag(Prefix,N1),
32		string_concatenate(Prefix,'__',PreSep),
33		string_concatenate(PreSep,N1,V).
34		get_gensym_counter(Prefix,R) :- (flag(Prefix,Count) -> R=Count ; R=0).
35
36		:- dynamic gennum_count/1.
37		gennum_count(0).
38
39		gennum(Nr) :-
40		retract(gennum_count(Nr)), N1 is Nr + 1,
41		assert(gennum_count(N1)).
42
43		reset_gensym :- retractall(flag(_,_)).
44		reset_gennum :- reset_gennum(0).
45
46		reset_gennum(Nr) :- retractall(gennum_count(_)), assert(gennum_count(Nr)).
47
48		oldvalue(Prefix,N) :- flag(Prefix,N),!.
49		oldvalue(_Prefix,0).
50		set_flag(Name,X) :-
51		nonvar(Name),
52		retract(flag(Name,_Val)),!,
53		asserta(flag(Name,X)).
54		set_flag(Name,X) :-
55		nonvar(Name),
56		asserta(flag(Name,X)).
57
58		:- dynamic flag/2.
59		%flag(foo,foo) :- fail.
60