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) 2006-2018, 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(error, 37 [ type_error/2, % +Type, +Term 38 domain_error/2, % +Domain, +Term 39 existence_error/2, % +Type, +Term 40 existence_error/3, % +Type, +Term, +Set 41 permission_error/3, % +Action, +Type, +Term 42 instantiation_error/1, % +Term 43 uninstantiation_error/1, % +Term 44 representation_error/1, % +Reason 45 syntax_error/1, % +Culprit 46 resource_error/1, % +Culprit 47 48 must_be/2, % +Type, +Term 49 is_of_type/2, % +Type, +Term 50 current_type/3 % ?Type, @Var, -Body 51 ]). 52:- set_prolog_flag(generate_debug_info, false).
70:- multifile 71 has_type/2. 72 73 /******************************* 74 * ISO ERRORS * 75 *******************************/
Suppose an argument must be a non-negative integer. If the actual argument is not an integer, this is a type_error. If it is a negative integer, it is a domain_error.
Typical borderline cases are predicates accepting a compound
term, e.g., point(X,Y). One could argue that the basic type is a
compound-term and any other compound term is a domain error.
Most Prolog programmers consider each compound as a type and
would consider a compound that is not point(_,_) a type_error.
94type_error(Type, Term) :-
95 throw(error(type_error(Type, Term), _)).
104domain_error(Type, Term) :-
105 throw(error(domain_error(Type, Term), _)).
112existence_error(Type, Term) :-
113 throw(error(existence_error(Type, Term), _)).
123existence_error(Type, Term, Set) :-
124 throw(error(existence_error(Type, Term, Set), _)).
131permission_error(Action, Type, Term) :-
132 throw(error(permission_error(Action, Type, Term), _)).
146instantiation_error(_Term) :-
147 throw(error(instantiation_error, _)).open(File, read, input) cannot succeed because the system
will allocate a new unique stream handle that will never unify
with input.
157uninstantiation_error(Term) :-
158 throw(error(uninstantiation_error(Term), _)).
168representation_error(Reason) :-
169 throw(error(representation_error(Reason), _)).
180syntax_error(Culprit) :-
181 throw(error(syntax_error(Culprit), _)).187resource_error(Culprit) :- 188 throw(error(resource_error(Culprit), _)). 189 190 191 /******************************* 192 * MUST-BE * 193 *******************************/
atom, atomic, between, boolean, callable,
chars, codes, text, compound, constant, float,
integer, nonneg, positive_integer, negative_integer,
nonvar, number, oneof, list, list_or_partial_list,
symbol, var, rational, encoding, dict and string.
Most of these types are defined by an arity-1 built-in predicate of the same name. Below is a brief definition of the other types.
| acyclic | Acyclic term (tree); see acyclic_term/1 |
| any | |
between(FloatL,FloatU) | Number [FloatL..FloatU] |
between(IntL,IntU) | Integer [IntL..IntU] |
| boolean | One of true or false |
| char | Atom of length 1 |
| chars | Proper list of 1-character atoms |
| code | Representation Unicode code point |
| codes | Proper list of Unicode character codes |
| constant | Same as atomic |
| cyclic | Cyclic term (rational tree); see cyclic_term/1 |
| dict | A dictionary term; see is_dict/1 |
| encoding | Valid name for a character encoding; see current_encoding/1 |
| list | A (non-open) list; see is_list/1 |
| negative_integer | Integer < 0 |
| nonneg | Integer >= 0 |
oneof(L) | Ground term that is member of L |
| positive_integer | Integer > 0 |
| proper_list | Same as list |
list(Type) | Proper list with elements of Type |
| list_or_partial_list | A list or an open list (ending in a variable); see is_list_or_partial_list/1 |
| stream | A stream name or valid stream handle; see is_stream/1 |
| symbol | Same as atom |
| text | One of atom, string, chars or codes |
| type | Term is a valid type specification |
Note: The Windows version can only represent Unicode code points up to 2^16-1. Higher values cause a representation error on most text handling predicates.
241must_be(Type, X) :-
242 ( nonvar(Type),
243 has_type(Type, X)
244 -> true
245 ; nonvar(Type)
246 -> is_not(Type, X)
247 ; instantiation_error(Type)
248 ).258is_not(list, X) :- 259 !, 260 not_a_list(list, X). 261is_not(list(Of), X) :- 262 !, 263 not_a_list(list(Of), X). 264is_not(list_or_partial_list, X) :- 265 !, 266 type_error(list, X). 267is_not(chars, X) :- 268 !, 269 not_a_list(list(char), X). 270is_not(codes, X) :- 271 !, 272 not_a_list(list(code), X). 273is_not(var,X) :- 274 !, 275 uninstantiation_error(X). 276is_not(cyclic, X) :- 277 domain_error(cyclic_term, X). 278is_not(acyclic, X) :- 279 domain_error(acyclic_term, X). 280is_not(Type, X) :- 281 ( var(X) 282 -> instantiation_error(X) 283 ; ground_type(Type), \+ ground(X) 284 -> instantiation_error(X) 285 ; current_type(Type, _Var, _Body) 286 -> type_error(Type, X) 287 ; existence_error(type, Type) 288 ). 289 290ground_type(ground). 291ground_type(oneof(_)). 292ground_type(stream). 293ground_type(text). 294ground_type(string). 295ground_type(rational). 296 297not_a_list(Type, X) :- 298 '$skip_list'(_, X, Rest), 299 ( var(Rest) 300 -> instantiation_error(X) 301 ; Rest == [] 302 -> Type = list(Of), 303 ( nonvar(Of) 304 -> element_is_not(X, Of) 305 ; instantiation_error(Of) 306 ) 307 ; type_error(Type, X) 308 ). 309 310 311element_is_not([H|T], Of) :- 312 has_type(Of, H), 313 !, 314 element_is_not(T, Of). 315element_is_not([H|_], Of) :- 316 !, 317 is_not(Of, H). 318element_is_not(_List, _Of) :- 319 assertion(fail).
325is_of_type(Type, Term) :- 326 nonvar(Type), 327 !, 328 has_type(Type, Term), 329 !. 330is_of_type(Type, _) :- 331 instantiation_error(Type).
337:- '$clausable'(has_type/2). % always allow clause/2 338 339has_type(any, _). 340has_type(atom, X) :- atom(X). 341has_type(atomic, X) :- atomic(X). 342has_type(between(L,U), X) :- ( integer(L) 343 -> integer(X), between(L,U,X) 344 ; number(X), X >= L, X =< U 345 ). 346has_type(boolean, X) :- (X==true;X==false), !. 347has_type(callable, X) :- callable(X). 348has_type(char, X) :- '$is_char'(X). 349has_type(code, X) :- '$is_char_code'(X). 350has_type(chars, X) :- '$is_char_list'(X, _Len). 351has_type(codes, X) :- '$is_code_list'(X, _Len). 352has_type(text, X) :- text(X). 353has_type(compound, X) :- compound(X). 354has_type(constant, X) :- atomic(X). 355has_type(float, X) :- float(X). 356has_type(ground, X) :- ground(X). 357has_type(cyclic, X) :- cyclic_term(X). 358has_type(acyclic, X) :- acyclic_term(X). 359has_type(integer, X) :- integer(X). 360has_type(nonneg, X) :- integer(X), X >= 0. 361has_type(positive_integer, X) :- integer(X), X > 0. 362has_type(negative_integer, X) :- integer(X), X < 0. 363has_type(nonvar, X) :- nonvar(X). 364has_type(number, X) :- number(X). 365has_type(oneof(L), X) :- ground(X), \+ \+ memberchk(X, L). 366has_type(proper_list, X) :- is_list(X). 367has_type(list, X) :- is_list(X). 368has_type(list_or_partial_list, X) :- is_list_or_partial_list(X). 369has_type(symbol, X) :- atom(X). 370has_type(var, X) :- var(X). 371has_type(rational, X) :- rational(X). 372has_type(string, X) :- string(X). 373has_type(stream, X) :- is_stream(X). 374has_type(encoding, X) :- current_encoding(X). 375has_type(dict, X) :- is_dict(X). 376has_type(list(Type), X) :- is_list(X), element_types(X, Type). 377has_type(type, Type) :- ground(Type), current_type(Type,_,_). 378 379text(X) :- 380 ( atom(X) 381 ; string(X) 382 ; '$is_char_list'(X, _) 383 ; '$is_code_list'(X, _) 384 ), 385 !. 386 387element_types(List, Type) :- 388 nonvar(Type), 389 !, 390 element_types_(List, Type). 391element_types(_List, Type) :- 392 instantiation_error(Type). 393 394element_types_([], _). 395element_types_([H|T], Type) :- 396 has_type(Type, H), 397 !, 398 element_types_(T, Type). 399 400is_list_or_partial_list(L0) :- 401 '$skip_list'(_, L0,L), 402 ( var(L) -> true ; L == [] ).
409current_encoding(octet). 410current_encoding(ascii). 411current_encoding(iso_latin_1). 412current_encoding(text). 413current_encoding(utf8). 414current_encoding(unicode_be). 415current_encoding(unicode_le). 416current_encoding(wchar_t).
424current_type(Type, Var, Body) :- 425 clause(has_type(Type, Var), Body0), 426 qualify(Body0, Body). 427 428qualify(Var, VarQ) :- 429 var(Var), 430 !, 431 VarQ = Var. 432qualify((A0,B0), (A,B)) :- 433 qualify(A0, A), 434 qualify(B0, B). 435qualify(G0, G) :- 436 predicate_property(system:G0, built_in), 437 !, 438 G = G0. 439qualify(G, error:G). 440 441 442 /******************************* 443 * SANDBOX * 444 *******************************/ 445 446:- multifile sandbox:safe_primitive/1. 447 448sandbox:safe_primitive(error:current_type(_,_,_))
Error generating support
This module provides predicates to simplify error generation and checking. It's implementation is based on a discussion on the SWI-Prolog mailinglist on best practices in error handling. The utility predicate must_be/2 provides simple run-time type validation. The *_error predicates are simple wrappers around throw/1 to simplify throwing the most common ISO error terms.
library(debug)andlibrary(prolog_stack).