1/* Part of SWI-Prolog 2 3 Author: Jan Wielemaker 4 E-mail: J.Wielemaker@vu.nl 5 WWW: http://www.swi-prolog.org 6 Copyright (c) 2004-2016, University of Amsterdam 7 VU University Amsterdam 8 All rights reserved. 9 10 Redistribution and use in source and binary forms, with or without 11 modification, are permitted provided that the following conditions 12 are met: 13 14 1. Redistributions of source code must retain the above copyright 15 notice, this list of conditions and the following disclaimer. 16 17 2. Redistributions in binary form must reproduce the above copyright 18 notice, this list of conditions and the following disclaimer in 19 the documentation and/or other materials provided with the 20 distribution. 21 22 THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 23 "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 24 LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 25 FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 26 COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 27 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 28 BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 29 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 30 CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31 LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 32 ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 33 POSSIBILITY OF SUCH DAMAGE. 34*/ 35 36:- module('$attvar', 37 [ '$wakeup'/1, % +Wakeup list 38 freeze/2, % +Var, :Goal 39 frozen/2, % @Var, -Goal 40 call_residue_vars/2, % :Goal, -Vars 41 copy_term/3 % +Term, -Copy, -Residue 42 ]).
56'$wakeup'([]). 57'$wakeup'(wakeup(Attribute, Value, Rest)) :- 58 call_all_attr_uhooks(Attribute, Value), 59 '$wakeup'(Rest). 60 61call_all_attr_uhooks([], _). 62call_all_attr_uhooks(att(Module, AttVal, Rest), Value) :- 63 uhook(Module, AttVal, Value), 64 call_all_attr_uhooks(Rest, Value).
This predicate deals with reserved attribute names to avoid the meta-call overhead.
76uhook(freeze, Goal, Y) :- 77 !, 78 ( attvar(Y) 79 -> ( get_attr(Y, freeze, G2) 80 -> put_attr(Y, freeze, '$and'(G2, Goal)) 81 ; put_attr(Y, freeze, Goal) 82 ) 83 ; unfreeze(Goal) 84 ). 85uhook(Module, AttVal, Value) :- 86 Module:attr_unify_hook(AttVal, Value).
freeze(X, (a, !, b)).98unfreeze('$and'(A,B)) :- 99 !, 100 unfreeze(A), 101 unfreeze(B). 102unfreeze(Goal) :- 103 .
109:- meta_predicate 110 freeze(, ). 111 112freeze(Var, Goal) :- 113 '$freeze'(Var, Goal), 114 !. % Succeeds if delayed 115freeze(_, Goal) :- 116 .
Note that attribute_goals//1 may destructively update attributes, often used to simplify the produced attributes. For frozen/2 however we must keep the original variables. Ideally we would demand attribute_goals//1 to not modify any attributes. As that is hard given where we are we now copy the result and fail, restoring the bindings. This is a simplified version of bagof/3.
130frozen(Term, Goal) :- 131 term_attvars(Term, AttVars), 132 ( AttVars == [] 133 -> Goal = true 134 ; sort(AttVars, AttVars2), 135 '$term_attvar_variables'(Term, KVars), 136 Keep =.. [v|KVars], 137 findall(Keep+Goal0, 138 frozen_residuals(AttVars2, Goal0), 139 [Kept+Goal]), 140 rebind_vars(Keep, Kept) 141 ). 142 143frozen_residuals(AttVars, Goal) :- 144 phrase(attvars_residuals(AttVars), GoalList0), 145 sort(GoalList0, GoalList), 146 make_conjunction(GoalList, Goal).
processed. We do not rebind such variables as
that would trigger constraints. These variables should not appear in
the produced goal anyway. If both are attvars, unifying may also
re-trigger. Therefore, we remove the variables from the copy before
rebinding. This should be ok as all variable identifies are properly
restored.160rebind_vars(Keep, Kept) :- 161 functor(Keep, _, Arity), 162 rebind_vars(1, Arity, Keep, Kept). 163 164rebind_vars(I, Arity, KeepT, KeptT) :- 165 I =< Arity, 166 !, 167 arg(I, KeepT, Keep), 168 arg(I, KeptT, Kept), 169 ( attvar(Keep), attvar(Kept) 170 -> del_attrs(Kept), 171 Keep = Kept 172 ; var(Kept) 173 -> Keep = Kept 174 ; true 175 ), 176 I2 is I+1, 177 rebind_vars(I2, Arity, KeepT, KeptT). 178rebind_vars(_, _, _, _). 179 180make_conjunction([], true). 181make_conjunction([H|T], Goal) :- 182 ( T == [] 183 -> Goal = H 184 ; Goal = (H,G), 185 make_conjunction(T, G) 186 ). 187 188 189 /******************************* 190 * PORTRAY * 191 *******************************/
attributes(portray) or
when the prolog flag write_attributes equals portray. Its task
is the write the attributes in a human readable format.199:- public 200 portray_attvar/1. 201 202portray_attvar(Var) :- 203 write('{'), 204 get_attrs(Var, Attr), 205 portray_attrs(Attr, Var), 206 write('}'). 207 208portray_attrs([], _). 209portray_attrs(att(Name, Value, Rest), Var) :- 210 portray_attr(Name, Value, Var), 211 ( Rest == [] 212 -> true 213 ; write(', '), 214 portray_attrs(Rest, Var) 215 ). 216 217portray_attr(freeze, Goal, Var) :- 218 !, 219 Options = [ portray(true), 220 quoted(true), 221 attributes(ignore) 222 ], 223 format('freeze(~W, ~W)', [ Var, Options, Goal, Options 224 ]). 225portray_attr(Name, Value, Var) :- 226 G = Name:attr_portray_hook(Value, Var), 227 ( '$c_current_predicate'(_, G), 228 229 -> true 230 ; format('~w = ...', [Name]) 231 ). 232 233 234 /******************************* 235 * CALL RESIDUE * 236 *******************************/
250:- meta_predicate 251 call_residue_vars(, ). 252 253call_residue_vars(Goal, Vars) :- 254 prolog_current_choice(Chp), 255 setup_call_cleanup( 256 '$call_residue_vars_start', 257 run_crv(Goal, Chp, Vars, Det), 258 '$call_residue_vars_end'), 259 ( Det == true 260 -> ! 261 ; true 262 ). 263call_residue_vars(_, _) :- 264 fail. 265 266run_crv(Goal, Chp, Vars, Det) :- 267 call(Goal), 268 deterministic(Det), 269 '$attvars_after_choicepoint'(Chp, Vars).
279copy_term(Term, Copy, Gs) :- 280 term_attvars(Term, Vs), 281 ( Vs == [] 282 -> Gs = [], 283 copy_term(Term, Copy) 284 ; sort(Vs, Vs2), 285 findall(Term-Gs, 286 ( phrase(attvars_residuals(Vs2), Gs), 287 delete_attributes(Term) 288 ), 289 [Copy-Gs]) 290 ). 291 292attvars_residuals([]) --> []. 293attvars_residuals([V|Vs]) --> 294 ( { get_attrs(V, As) } 295 -> attvar_residuals(As, V) 296 ; [] 297 ), 298 attvars_residuals(Vs). 299 300attvar_residuals([], _) --> []. 301attvar_residuals(att(Module,Value,As), V) --> 302 ( { nonvar(V) } 303 -> % a previous projection predicate could have instantiated 304 % this variable, for example, to avoid redundant goals 305 [] 306 ; ( { Module == freeze } 307 -> frozen_residuals(Value, V) 308 ; { current_predicate(Module:attribute_goals//1), 309 phrase(Module:attribute_goals(V), Goals) 310 } 311 -> list(Goals) 312 ; [put_attr(V, Module, Value)] 313 ) 314 ), 315 attvar_residuals(As, V). 316 317list([]) --> []. 318list([L|Ls]) --> [L], list(Ls). 319 320delete_attributes(Term) :- 321 term_attvars(Term, Vs), 322 delete_attributes_(Vs). 323 324delete_attributes_([]). 325delete_attributes_([V|Vs]) :- 326 del_attrs(V), 327 delete_attributes_(Vs).
freeze(X, a), freeze(X, !) would create freeze(X,
(a,!)), which is fundamentally different. We could create
freeze(X, (call(a), call(!))) or preform a more eleborate
analysis to validate the semantics are not changed.339frozen_residuals('$and'(X,Y), V) --> 340 !, 341 frozen_residuals(X, V), 342 frozen_residuals(Y, V). 343frozen_residuals(X, V) --> 344 [ freeze(V, X) ]
Attributed variable handling
Attributed variable and coroutining support based on attributed variables. This module is complemented with C-defined predicates defined in pl-attvar.c */