Category : Miscellaneous Language Source Code
Archive   : PROLOG19.ZIP
Filename : GENSYM.PRO

/* Makes new atoms, one at a time. Do not expect a repeat solution.
You must ask each time you want an atom. It starts with some root,
and appends an incrementing number onto it.

Ask: ?-gensym( student, X ). get: X = student1.
?-gensym( student, X ). get: X = student2.
?-gensym( student, X ). get: X = student3.

and ad infinitum. */

gensym( Root, Atom ) :-
get_num( Root, Num ),
name( Root, Name1 ),
integer_name( Num, Name2 ),
append( Name1, Name2, Name ),
name( Atom, Name ).

get_num( Root, Num ) :-
retract( current_num( Root, Num1 )), !,
Num is Num1 + 1,
asserta( current_num( Root, Num)).

get_num( Root, 1 ) :- asserta( current_num( Root, 1 )).

integer_name( Int, List ) :- integer_name( Int, [], List ).
integer_name( I, Sofar, [C|Sofar] ) :-
I < 10, !, C is I + 48.
integer_name( I, Sofar, List ) :-
Tophalf is I/10,
Bothalf is I mod 10,
C is Bothalf + 48,
integer_name( Tophalf, [C|Sofar], List ).


append( [], L, L ).
append( [Z|L1], L2, [Z|L3] ) :- append( L1, L2, L3 ).

printstring( [] ).
printstring( [] ).
printstring( [H|T] ) :- put( H ), printstring( T ).