/usr/share/Yap/coinduction.yap is in yap 6.2.2-6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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* *
* YAP Prolog *
* *
* Yap Prolog was developed at NCCUP - Universidade do Porto *
* *
* Copyright L.Damas, V.S.Costa and Universidade do Porto 1985-1997 *
* *
**************************************************************************
* *
* File: atts.yap *
* Last rev: 8/2/88 *
* mods: *
* comments: attribute support for Prolog *
* *
*************************************************************************/
% :- yap_flag(unknown,error).
% :- style_check(all).
%
% Code originally written by Arvin Bansal and Vitor Santos Costa
% Includes nice extensions from Jan Wielemaker (from the SWI version).
%
:- module(coinduction,
[ (coinductive)/1,
op(1150, fx, (coinductive))
]).
:- use_module(library(error)).
/** <module> Co-Logic Programming
This simple module implements the directive coinductive/1 as described
in "Co-Logic Programming: Extending Logic Programming with Coinduction"
by Luke Somin et al. The idea behind coinduction is that a goal succeeds
if it unifies to a parent goal. This enables some interesting programs,
notably on infinite trees (cyclic terms).
==
:- use_module(library(coinduction)).
:- coinductive stream/1.
stream([H|T]) :- i(H), stream(T).
% inductive
i(0).
i(s(N)) :- i(N).
?- X=[s(s(A))|X], stream(X).
X= [s(s(A))|X], stream(X).
A = 0,
X = [s(s(0)),**]
==
This predicate is true for any cyclic list containing only 1-s,
regardless of the cycle-length.
@bug Programs mixing normal predicates and coinductive predicates must
be _stratified_. The theory does not apply to normal Prolog calling
coinductive predicates, calling normal Prolog predicates, etc.
Stratification is not checked or enforced in any other way and thus
left as a responsibility to the user.
@see "Co-Logic Programming: Extending Logic Programming with Coinduction"
by Luke Somin et al.
*/
:- meta_predicate coinductive(:).
:- dynamic coinductive/3.
%-----------------------------------------------------
coinductive(Spec) :-
var(Spec),
!,
throw(error(instantiation_error,coinductive(Spec))).
coinductive(Module:Spec) :-
coinductive_declaration(Spec, Module, coinductive(Module:Spec)).
coinductive(Spec) :-
prolog_load_context(module, Module),
coinductive_declaration(Spec, Module, coinductive(Spec)).
coinductive_declaration(Spec, _M, G) :-
var(Spec),
!,
throw(error(instantiation_error,G)).
coinductive_declaration((A,B), M, G) :- !,
coinductive_declaration(A, M, G),
coinductive_declaration(B, M, G).
coinductive_declaration(M:Spec, _, G) :- !,
coinductive_declaration(Spec, M, G).
coinductive_declaration(Spec, M, _G) :-
valid_pi(Spec, F, N),
functor(S,F,N),
atomic_concat(['__coinductive__',F,'/',N],NF),
functor(NS,NF,N),
match_args(N,S,NS),
atomic_concat(['__stack_',M,':',F,'/',N],SF),
nb_setval(SF, _),
assert((M:S :-
b_getval(SF,L),
coinduction:in_stack(S, L, End),
(
nonvar(End)
->
true
;
End = [S|_],
M:NS)
)
),
assert(coinduction:coinductive(S,M,NS)).
valid_pi(Name/Arity, Name, Arity) :-
must_be(atom, Name),
must_be(integer, Arity).
match_args(0,_,_) :- !.
match_args(I,S1,S2) :-
arg(I,S1,A),
arg(I,S2,A),
I1 is I-1,
match_args(I1,S1,S2).
%-----------------------------------------------------
co_term_expansion((M:H :- B), _, (M:NH :- B)) :- !,
co_term_expansion((H :- B), M, (NH :- B)).
co_term_expansion((H :- B), M, (NH :- B)) :- !,
coinductive(H, M, NH), !.
co_term_expansion(H, M, NH) :-
coinductive(H, M, NH), !.
user:term_expansion(M:Cl,M:NCl ) :- !,
co_term_expansion(Cl, M, NCl).
user:term_expansion(G, NG) :-
prolog_load_context(module, Module),
co_term_expansion(G, Module, NG).
%-----------------------------------------------------
in_stack(_, V, V) :- var(V), !.
in_stack(G, [G|_], [G|_]) :- !.
in_stack(G, [_|T], End) :- in_stack(G, T, End).
writeG_val(G_var) :-
b_getval(G_var, G_val),
write(G_var), write(' ==> '), write(G_val), nl.
%-----------------------------------------------------
/**************************************
Some examples from Coinductive Logic Programming and its Applications by Gopal Gupta et al, ICLP 97
:- coinductive stream/1.
stream([H|T]) :- i(H), stream(T).
% inductive
i(0).
i(s(N)) :- i(N).
**************************************/
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