/* Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: J.Wielemaker@vu.nl
WWW: http://www.swi-prolog.org
Copyright (c) 2006-2016, University of Amsterdam
VU University Amsterdam
All rights reserved.
Redistribution and use in source and binary forms, with or without
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,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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*/
:- module(error,
[ type_error/2, % +Type, +Term
domain_error/2, % +Domain, +Term
existence_error/2, % +Type, +Term
permission_error/3, % +Action, +Type, +Term
instantiation_error/1, % +Term
uninstantiation_error/1, % +Term
representation_error/1, % +Reason
syntax_error/1, % +Culprit
resource_error/1, % +Culprit
must_be/2, % +Type, +Term
is_of_type/2, % +Type, +Term
current_type/3 % ?Type, @Var, -Body
]).
:- set_prolog_flag(generate_debug_info, false).
/** <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(+Type, +Term).
%
% Tell the user that Term is not of the expected Type. 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 compoint that is not point(_,_) a _type_error_.
type_error(Type, Term) :-
throw(error(type_error(Type, Term), _)).
%! domain_error(+Type, +Term).
%
% 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(Type, Term) :-
throw(error(domain_error(Type, Term), _)).
%! existence_error(+Type, +Term).
%
% Term is of the correct type and correct domain, but there is no
% existing (external) resource that is represented by it.
existence_error(Type, Term) :-
throw(error(existence_error(Type, Term), _)).
%! permission_error(+Action, +Type, +Term).
%
% It is not allowed to perform Action on the object Term that is
% of the given Type.
permission_error(Action, Type, Term) :-
throw(error(permission_error(Action, Type, Term), _)).
%! instantiation_error(+Term).
%
% 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.
%
% @param Term 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(_Term) :-
throw(error(instantiation_error, _)).
%! uninstantiation_error(+Term)
%
% 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(Term) :-
throw(error(uninstantiation_error(Term), _)).
%! representation_error(+Reason).
%
% 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(Reason) :-
throw(error(representation_error(Reason), _)).
%! syntax_error(+Culprit)
%
% A text has invalid syntax. The error is described by Culprit.
%
% @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(+Culprit)
%
% A goal cannot be completed due to lack of resources.
resource_error(Culprit) :-
throw(error(resource_error(Culprit), _)).
/*******************************
* 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.
%
% | boolean | one of =true= or =false= |
% | char | Atom of length 1 |
% | code | Representation Unicode code point |
% | chars | Proper list of 1-character atoms |
% | codes | Proper list of Unicode character codes |
% | text | One of =atom=, =string=, =chars= or =codes= |
% | between(IntL,IntU) | Integer [IntL..IntU] |
% | between(FloatL,FloatU) | Number [FloatL..FloatU] |
% | nonneg | Integer >= 0 |
% | positive_integer | Integer > 0 |
% | negative_integer | Integer < 0 |
% | oneof(L) | Ground term that is member of L |
% | encoding | Valid name for a character encoding |
% | cyclic | Cyclic term (rational tree) |
% | acyclic | Acyclic term (tree) |
% | list(Type) | Proper list with elements of Type |
% | list_or_partial_list | A list or an open list (ending in a variable |
%
% 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.
%
% @throws 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) :-
( var(X)
-> instantiation_error(X)
; ground_type(Type), \+ ground(X)
-> instantiation_error(X)
; current_type(Type, _Var, _Body)
-> type_error(Type, X)
; 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
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(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(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).
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_([], _).
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).
/*******************************
* SANDBOX *
*******************************/
:- multifile sandbox:safe_primitive/1.
sandbox:safe_primitive(error:current_type(_,_,_)).