/* Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: J.Wielemaker@vu.nl
WWW: http://www.swi-prolog.org
Copyright (c) 2006-2024, University of Amsterdam
VU University Amsterdam
SWI-Prolog Solutions b.v.
All rights reserved.
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modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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*/
:- module(error,
[ instantiation_error/1, % +FormalSubTerm
uninstantiation_error/1, % +Culprit
type_error/2, % +ValidType, +Culprit
domain_error/2, % +ValidDomain, +Culprit
existence_error/2, % +ObjectType, +Culprit
existence_error/3, % +ObjectType, +Culprit, +Set
permission_error/3, % +Operation, +PermissionType, +Culprit
representation_error/1, % +Flag
resource_error/1, % +Resource
syntax_error/1, % +ImplDepAtom
must_be/2, % +Type, +Term
is_of_type/2, % +Type, +Term
current_type/3 % ?Type, @Var, -Body
]).
:- set_prolog_flag(generate_debug_info, false).
:- use_module(library(debug), [assertion/1]).
/** <module> 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.
@author Jan Wielemaker
@author Richard O'Keefe
@author Ulrich Neumerkel
@see library(debug) and library(prolog_stack).
@see print_message/2 is used to print (uncaught) error terms.
*/
:- multifile
has_type/2.
/*******************************
* ISO ERRORS *
*******************************/
%! type_error(+ValidType, +Culprit).
%
% Tell the user that Culprit is not of the expected ValidType. This
% error is closely related to domain_error/2 because the notion of
% types is not really set in stone in Prolog. We introduce the
% difference using a simple example.
%
% 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_.
type_error(ValidType, Culprit) :-
throw(error(type_error(ValidType, Culprit), _)).
%! domain_error(+ValidDomain, +Culprit).
%
% The argument is of the proper type, but has a value that is outside
% the supported values. See type_error/2 for a more elaborate
% discussion of the distinction between type- and domain-errors.
domain_error(ValidDomain, Culprit) :-
throw(error(domain_error(ValidDomain, Culprit), _)).
%! existence_error(+ObjectType, +Culprit).
%
% Culprit is of the correct type and correct domain, but there is no
% existing (external) resource of type ObjectType that is represented
% by it.
existence_error(ObjectType, Culprit) :-
throw(error(existence_error(ObjectType, Culprit), _)).
%! existence_error(+ObjectType, +Culprit, +Set).
%
% Culprit is of the correct type and correct domain, but there is no
% existing (external) resource of type ObjectType that is represented
% by it in the provided set. The thrown exception term carries a
% formal term structured as follows: existence_error(ObjectType,
% Culprit, Set)
%
% @compat This error is outside the ISO Standard.
existence_error(ObjectType, Culprit, Set) :-
throw(error(existence_error(ObjectType, Culprit, Set), _)).
%! permission_error(+Operation, +PermissionType, +Culprit).
%
% It is not allowed to perform Operation on (whatever is represented
% by) Culprit that is of the given PermissionType (in fact, the ISO
% Standard is confusing and vague about these terms' meaning).
permission_error(Operation, PermissionType, Culprit) :-
throw(error(permission_error(Operation, PermissionType, Culprit), _)).
%! instantiation_error(+FormalSubTerm).
%
% An argument is under-instantiated. I.e. it is not acceptable as it
% is, but if some variables are bound to appropriate values it would
% be acceptable.
%
% @arg FormalSubTerm is the term that needs (further)
% instantiation. Unfortunately, the ISO error does not allow
% for passing this term along with the error, but we pass it
% to this predicate for documentation purposes and to allow
% for future enhancement.
instantiation_error(_FormalSubTerm) :-
throw(error(instantiation_error, _)).
%! uninstantiation_error(+Culprit)
%
% An argument is over-instantiated. This error is used for output
% arguments whose value cannot be known upfront. For example, the goal
% open(File, read, input) cannot succeed because the system will
% allocate a new unique stream handle that will never unify with
% `input`.
uninstantiation_error(Culprit) :-
throw(error(uninstantiation_error(Culprit), _)).
%! representation_error(+Flag).
%
% A representation error indicates a limitation of the implementation.
% SWI-Prolog has no such limits that are not covered by other errors,
% but an example of a representation error in another Prolog
% implementation could be an attempt to create a term with an arity
% higher than supported by the system.
representation_error(Flag) :-
throw(error(representation_error(Flag), _)).
%! syntax_error(+Culprit)
%
% A text has invalid syntax. The error is described by Culprit.
% According to the ISO Standard, Culprit should be an
% implementation-dependent atom.
%
% @tbd Deal with proper description of the location of the
% error. For short texts, we allow for Type(Text), meaning
% Text is not a valid Type. E.g. syntax_error(number('1a'))
% means that =1a= is not a valid number.
syntax_error(Culprit) :-
throw(error(syntax_error(Culprit), _)).
%! resource_error(+Resource)
%
% A goal cannot be completed due to lack of resources. According to
% the ISO Standard, Resource should be an implementation-dependent
% atom.
resource_error(Resource) :-
throw(error(resource_error(Resource), _)).
/*******************************
* MUST-BE *
*******************************/
%! must_be(+Type, @Term) is det.
%
% True if Term satisfies the type constraints for Type. Defined
% types are `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 | any term |
% | between(FloatL,FloatU) | Number [FloatL..FloatU] |
% | between(IntL,IntU) | Integer [IntL..IntU] |
% | boolean | One of `true` or `false` |
% | callable | Atom or compound term |
% | char | Atom of length 1 |
% | chars | Proper list of 1-character atoms |
% | code | Representation Unicode code point (0..0x10ffff) |
% | codes | Proper list of Unicode character codes |
% | compound | compound term |
% | compound(Term) | Compound with same name/arity as term; checks arguments |
% | 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 |
% | 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 |
% | negative_integer | Integer < 0 |
% | nonneg | Integer >= 0 |
% | oneof(L) | Ground term that is member of L |
% | pair | Key-Value pair. Same as compound(any-any) |
% | positive_integer | Integer > 0 |
% | proper_list | Same as list |
% | 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 |
%
% In addition, types may be composed using `TypeA,TypeB`,
% `TypeA;TypeB` and negated using `\Type`.
%
% @error instantiation_error if Term is insufficiently
% instantiated and type_error(Type, Term) if Term is not of Type.
must_be(Type, X) :-
( nonvar(Type),
has_type(Type, X)
-> true
; nonvar(Type)
-> is_not(Type, X)
; instantiation_error(Type)
).
%! is_not(+Type, @Term)
%
% Throws appropriate error. It is _known_ that Term is not of type
% Type.
%
% @throws type_error(Type, Term)
% @throws instantiation_error
is_not(list, X) :-
!,
not_a_list(list, X).
is_not(list(Of), X) :-
!,
not_a_list(list(Of), X).
is_not(list_or_partial_list, X) :-
!,
type_error(list, X).
is_not(chars, X) :-
!,
not_a_list(list(char), X).
is_not(codes, X) :-
!,
not_a_list(list(code), X).
is_not(var,X) :-
!,
uninstantiation_error(X).
is_not(cyclic, X) :-
domain_error(cyclic_term, X).
is_not(acyclic, X) :-
domain_error(acyclic_term, X).
is_not(Type, X) :-
current_type(Type, _Var, _Body),
!,
( var(X)
-> instantiation_error(X)
; ground_type(Type), \+ ground(X)
-> instantiation_error(X)
; type_error(Type, X)
).
is_not(Type, _) :-
existence_error(type, Type).
ground_type(ground).
ground_type(oneof(_)).
ground_type(stream).
ground_type(text).
ground_type(string).
ground_type(rational).
not_a_list(Type, X) :-
'$skip_list'(_, X, Rest),
( var(Rest)
-> instantiation_error(X)
; Rest == []
-> Type = list(Of),
( nonvar(Of)
-> element_is_not(X, Of)
; instantiation_error(Of)
)
; type_error(Type, X)
).
element_is_not([H|T], Of) :-
has_type(Of, H),
!,
element_is_not(T, Of).
element_is_not([H|_], Of) :-
!,
is_not(Of, H).
element_is_not(_List, _Of) :-
assertion(fail).
%! is_of_type(+Type, @Term) is semidet.
%
% True if Term satisfies Type.
is_of_type(Type, Term) :-
nonvar(Type),
!,
has_type(Type, Term),
!.
is_of_type(Type, _) :-
instantiation_error(Type).
%! has_type(+Type, @Term) is semidet.
%
% True if Term satisfies Type.
:- '$clausable'(has_type/2). % always allow clause/2
:- public % May be called through current_type/3
is_list_or_partial_list/1,
current_encoding/1,
element_types/2.
has_type(any, _).
has_type(atom, X) :- atom(X).
has_type(atomic, X) :- atomic(X).
has_type(between(L,U), X) :-
( integer(L)
-> integer(X), between(L,U,X)
; number(X), X >= L, X =< U
).
has_type(boolean, X) :- (X==true;X==false), !.
has_type(callable, X) :- callable(X).
has_type(char, X) :- '$is_char'(X).
has_type(code, X) :- '$is_char_code'(X).
has_type(chars, X) :- '$is_char_list'(X, _Len).
has_type(codes, X) :- '$is_code_list'(X, _Len).
has_type(text, X) :- text(X).
has_type(compound, X) :- compound(X).
has_type(compound(Term),X):- compound(X), is_term_of_type(Term,X).
has_type(constant, X) :- atomic(X).
has_type(float, X) :- float(X).
has_type(ground, X) :- ground(X).
has_type(cyclic, X) :- cyclic_term(X).
has_type(acyclic, X) :- acyclic_term(X).
has_type(integer, X) :- integer(X).
has_type(nonneg, X) :- integer(X), X >= 0.
has_type(positive_integer, X) :- integer(X), X > 0.
has_type(negative_integer, X) :- integer(X), X < 0.
has_type(nonvar, X) :- nonvar(X).
has_type(number, X) :- number(X).
has_type(oneof(L), X) :- ground(X), \+ \+ memberchk(X, L).
has_type(pair, X) :- nonvar(X), X = _-_.
has_type(proper_list, X) :- is_list(X).
has_type(list, X) :- is_list(X).
has_type(list_or_partial_list, X) :- is_list_or_partial_list(X).
has_type(symbol, X) :- atom(X).
has_type(var, X) :- var(X).
has_type(rational, X) :- rational(X).
has_type(string, X) :- string(X).
has_type(stream, X) :- is_stream(X).
has_type(encoding, X) :- current_encoding(X).
has_type(dict, X) :- is_dict(X).
has_type(list(Type), X) :- is_list(X), element_types(X, Type).
has_type(list_or_partial_list(Type), X) :- is_list_or_partial_list(X), element_types(X, Type).
has_type(type, Type) :- ground(Type), current_type(Type,_,_).
has_type((A,B), X) :- (is_of_type(A,X)->is_of_type(B,X)).
has_type((A;B), X) :- (is_of_type(A,X)->true;is_of_type(B,X)).
has_type(\A, X) :- \+ is_of_type(A,X).
text(X) :-
( atom(X)
; string(X)
; '$is_char_list'(X, _)
; '$is_code_list'(X, _)
),
!.
element_types(List, Type) :-
nonvar(Type),
!,
element_types_(List, Type).
element_types(_List, Type) :-
instantiation_error(Type).
element_types_(Var, _) :-
var(Var),
!.
element_types_([], _).
element_types_([H|T], Type) :-
has_type(Type, H),
!,
element_types_(T, Type).
is_list_or_partial_list(L0) :-
'$skip_list'(_, L0,L),
( var(L) -> true ; L == [] ).
%! current_encoding(?Name) is nondet.
%
% True if Name is the name of a supported encoding. See encoding
% option of e.g., open/4.
current_encoding(octet).
current_encoding(ascii).
current_encoding(iso_latin_1).
current_encoding(text).
current_encoding(utf8).
current_encoding(unicode_be).
current_encoding(unicode_le).
current_encoding(wchar_t).
%! current_type(?Type, @Var, -Body) is nondet.
%
% True when Type is a currently defined type and Var satisfies Type of
% the body term Body succeeds.
current_type(Type, Var, Body) :-
clause(has_type(Type, Var), Body0),
qualify(Body0, Body).
qualify(Var, VarQ) :-
var(Var),
!,
VarQ = Var.
qualify((A0,B0), (A,B)) :-
qualify(A0, A),
qualify(B0, B).
qualify(G0, G) :-
predicate_property(system:G0, built_in),
!,
G = G0.
qualify(G, error:G).
%! is_term_of_type(Term, X)
%
% Supports types as e.g. compound(oneof(list(atom))).
is_term_of_type(Term, X) :-
compound_name_arity(Term, N, A),
compound_name_arity(X, N, A),
term_arg_types(1, A, Term, X).
term_arg_types(I, A, Type, X) :-
I =< A,
!,
arg(I, Type, AType),
arg(I, X, XArg),
has_type(AType, XArg),
I2 is I+1,
term_arg_types(I2, A, Type, X).
term_arg_types(_, _, _, _).
/*******************************
* SANDBOX *
*******************************/
:- multifile sandbox:safe_primitive/1.
sandbox:safe_primitive(error:current_type(_,_,_)).