update docummentation.
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Vitor Santos Costa
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docs/swi.tex
191
docs/swi.tex
@ -1,8 +1,8 @@
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@chapter SWI-Prolog Emulation
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This library provides a number of SWI-Prolog builtins that are not by
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default in YAP. This library is loaded with the
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@code{use_module(library(swi))} command.
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default in YAP. This support is loaded with the
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@code{expects_dialect(swi)} command.
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@table @code
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@ -168,7 +168,7 @@ triple. See the example above.
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@c @var{Pred} applies.
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@end table
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@node Forall,hProlog and SWI-Prolog Attributed Variables,Invoking Predicates on all Members of a List, SWI-Prolog
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@node Forall, ,Invoking Predicates on all Members of a List, SWI-Prolog
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@section Forall
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@c \label{sec:forall2}
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@ -189,176 +189,8 @@ The next example verifies that all arithmetic statements in the list
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@end table
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@node hProlog and SWI-Prolog Attributed Variables, SWI-Prolog Global Variables, Forall,SWI-Prolog
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@section hProlog and SWI-Prolog Attributed Variables
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@cindex hProlog Attributed Variables
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Attributed variables
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@c @ref{Attributed variables}
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provide a technique for extending the
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Prolog unification algorithm by hooking the binding of attributed
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variables. There is little consensus in the Prolog community on the
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exact definition and interface to attributed variables. Yap Prolog
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traditionally implements a SICStus-like interface, but to enable
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SWI-compatibility we have implemented the SWI-Prolog interface,
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identical to the one realised by Bart Demoen for hProlog.
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Binding an attributed variable schedules a goal to be executed at the
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first possible opportunity. In the current implementation the hooks are
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executed immediately after a successful unification of the clause-head
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or successful completion of a foreign language (builtin) predicate. Each
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attribute is associated to a module and the hook (attr_unify_hook/2) is
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executed in this module. The example below realises a very simple and
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incomplete finite domain reasoner.
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@example
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:- module(domain,
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[ domain/2 % Var, ?Domain
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]).
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:- use_module(library(oset)).
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domain(X, Dom) :-
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var(Dom), !,
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get_attr(X, domain, Dom).
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domain(X, List) :-
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sort(List, Domain),
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put_attr(Y, domain, Domain),
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X = Y.
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% An attributed variable with attribute value Domain has been
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% assigned the value Y
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attr_unify_hook(Domain, Y) :-
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( get_attr(Y, domain, Dom2)
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-> oset_int(Domain, Dom2, NewDomain),
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( NewDomain == []
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-> fail
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; NewDomain = [Value]
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-> Y = Value
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; put_attr(Y, domain, NewDomain)
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)
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; var(Y)
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-> put_attr( Y, domain, Domain )
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; memberchk(Y, Domain)
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).
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@end example
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Before explaining the code we give some example queries:
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@table @code
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@item ?- domain(X, [a,b]), X = c
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no
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@item ?- domain(X, [a,b]), domain(X, [a,c]).
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X = a
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@item ?- domain(X, [a,b,c]), domain(X, [a,c]).
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X = _D0
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@end table
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The predicate @code{domain/2} fetches (first clause) or assigns
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(second clause) the variable a @emph{domain}, a set of values it can
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be unified with. In the second clause first associates the domain
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with a fresh variable and then unifies X to this variable to deal
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with the possibility that X already has a domain. The
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predicate @code{attr_unify_hook/2} is a hook called after a variable with
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a domain is assigned a value. In the simple case where the variable
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is bound to a concrete value we simply check whether this value is in
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the domain. Otherwise we take the intersection of the domains and either
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fail if the intersection is empty (first example), simply assign the
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value if there is only one value in the intersection (second example) or
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assign the intersection as the new domain of the variable (third
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example).
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@table @code
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@item put_attr(+@var{Var},+@var{Module},+@var{Value})
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@findex put_attr/3
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@snindex put_attr/3
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@cnindex put_attr/3
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If @var{Var} is a variable or attributed variable, set the value for the
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attribute named @var{Module} to @var{Value}. If an attribute with this
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name is already associated with @var{Var}, the old value is replaced.
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Backtracking will restore the old value (i.e. an attribute is a mutable
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term. See also @code{setarg/3}). This predicate raises a type error if
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@var{Var} is not a variable or @var{Module} is not an atom.
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@item get_attr(+@var{Var},+@var{Module},+@var{Value})
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@findex get_attr/3
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@snindex get_attr/3
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@cnindex get_attr/3
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Request the current @var{value} for the attribute named @var{Module}. If
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@var{Var} is not an attributed variable or the named attribute is not
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associated to @var{Var} this predicate fails silently. If @var{Module}
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is not an atom, a type error is raised.
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@item del_attr(+@var{Var},+@var{Module})
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@findex del_attr/2
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@snindex del_attr/2
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@cnindex del_attr/2
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Delete the named attribute. If @var{Var} loses its last attribute it
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is transformed back into a traditional Prolog variable. If @var{Module}
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is not an atom, a type error is raised. In all other cases this
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predicate succeeds regardless of whether or not the named attribute is
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present.
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@item attr_unify_hook(+@var{AttValue},+@var{VarValue})
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@findex attr_unify_hook/2
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@snindex attr_unify_hook/2
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@cnindex attr_unify_hook/2
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Hook that must be defined in the module an attributed variable refers
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to. It is called @emph{after} the attributed variable has been
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unified with a non-var term, possibly another attributed variable.
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@var{AttValue} is the attribute that was associated to the variable
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in this module and @var{VarValue} is the new value of the variable.
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Normally this predicate fails to veto binding the variable to
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@var{VarValue}, forcing backtracking to undo the binding. If
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@var{VarValue} is another attributed variable the hook often combines
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the two attribute and associates the combined attribute with
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@var{VarValue} using @code{put_attr/3}.
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@c \predicate{attr_portray_hook}{2}{+AttValue, +Var}
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@c Called by write_term/2 and friends for each attribute if the option
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@c \term{attributes}{portray} is in effect. If the hook succeeds the
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@c attribute is considered printed. Otherwise \exam{Module = ...} is
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@c printed to indicate the existence of a variable.
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@end table
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@subsection Special Purpose SWI Predicates for Attributes
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Normal user code should deal with @code{put_attr/3}, @code{get_attr/3}
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and @code{del_attr/2}. The routines in this section fetch or set the
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entire attribute list of a variables. Use of these predicates is
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anticipated to be restricted to printing and other special purpose
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operations.
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@table @code
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@item get_attrs(+@var{Var},-@var{Attributes})
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@findex get_attrs/2
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@snindex get_attrs/2
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@cnindex get_attrs/2
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Get all attributes of @var{Var}. @var{Attributes} is a term of the form
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@code{att(Module, Value, MoreAttributes)}, where @var{MoreAttributes} is
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@code{[]} for the last attribute.
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@item put_attrs(+@var{Var},+@var{Attributes})
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@findex put_attrs/2
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@snindex put_attrs/2
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@cnindex put_attrs/2
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Set all attributes of @var{Var}. See get_attrs/2 for a description of
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@var{Attributes}.
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@item copy_term_nat(?@var{TI},-@var{TF})
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@findex copy_term_nat/2
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@snindex copy_term_nat/2
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@cnindex copy_term_nat/2
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As @code{copy_term/2}. Attributes however, are @emph{not} copied but replaced
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by fresh variables.
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@end table
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@node SWI-Prolog Global Variables, ,hProlog and SWI-Prolog Attributed Variables,SWI-Prolog
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@section SWI Global variables
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@node SWI-Prolog Global Variables, Extensions, SWI-Prolog, Top
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@chapter SWI Global variables
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@c \label{sec:gvar}
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SWI-Prolog global variables are associations between names (atoms) and
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@ -478,11 +310,11 @@ enumeration is undefined.
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Delete the named global variable.
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@end table
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@subsection Compatibility of SWI-Prolog Global Variables
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@section Compatibility of Global Variables
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Global variables have been introduced by various Prolog
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implementations recently. The implementation of them in SWI-Prolog is
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based on hProlog by Bart Demoen. In discussion with Bart it was
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implementations recently. YAP follows their implementation in SWI-Prolog, itself
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based on hProlog by Bart Demoen. Jan and Bart
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decided that the semantics if hProlog @code{nb_setval/2}, which is
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equivalent to @code{nb_linkval/2} is not acceptable for normal Prolog
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users as the behaviour is influenced by how builtin predicates
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@ -493,10 +325,3 @@ Arrays can be implemented easily in SWI-Prolog using @code{functor/3} and
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@code{setarg/3} due to the unrestricted arity of compound terms.
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@node Extensions,Debugging,SWI-Prolog,Top
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@chapter Extensions to Prolog
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YAP includes several extensions that are not enabled by
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default, but that can be used to extend the functionality of the
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system. These options can be set at compilation time by enabling the
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related compilation flag, as explained in the @code{Makefile}
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318
docs/yap.tex
318
docs/yap.tex
@ -91,6 +91,7 @@ us to include his text in this document.
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* Built-ins:: Built In Predicates
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* Library:: Library Predicates
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* SWI-Prolog:: SWI-Prolog emulation
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* Global Variables :: Global Variables for Prolog
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* Extensions:: Extensions to Standard YAP
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* Rational Trees:: Working with Rational Trees
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* Co-routining:: Changing the Execution of Goals
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@ -242,7 +243,6 @@ Subnodes of Attributes
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Subnodes of SWI-Prolog
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* Invoking Predicates on all Members of a List :: maplist and friends
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* hProlog and SWI-Prolog Attributed Variables :: Emulating SWI-like attributed variables
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* SWI-Prolog Global Variables :: Emulating SWI-like attributed variables
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@c Subnodes of CLP(Q,R)
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@ -3317,22 +3317,6 @@ in @var{TI} are also duplicated.
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Also refer to @code{copy_term/2}.
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@item copy_term(?@var{TI},-@var{TF},-@var{Goals})
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@findex copy_term/3
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@syindex copy_term/3
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@cnindex copy_term/3
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Term @var{TF} is a variant of the original term @var{TI}, such that for
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each variable @var{V} in the term @var{TI} there is a new variable @var{V'}
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in term @var{TF} without any attributes attached. Attributed
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variables are thus converted to standard variables. @var{Goals} is
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unified with a list that represents the attributes. The goal
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@code{maplist(call,@var{Goals})} can be called to recreate the
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attributes.
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Before the actual copying, @code{copy_term/3} calls
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@code{attribute_goals/1} in the module where the attribute is
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defined.
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@end table
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@node Predicates on Atoms, Predicates on Characters, Testing Terms, Top
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@ -6567,7 +6551,7 @@ Execute a new shell.
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@snindex alarm/3
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@cnindex alarm/3
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Arranges for YAP to be interrupted in @var{Seconds} seconds, or in
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@var{[Seconds|MicroSeconds]}. When interrupted, YAP will execute
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[@var{Seconds}|@var{MicroSeconds}]. When interrupted, YAP will execute
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@var{Callable} and then return to the previous execution. If
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@var{Seconds} is @code{0}, no new alarm is scheduled. In any event,
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any previously set alarm is canceled.
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@ -12222,19 +12206,25 @@ are released.
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@end table
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@node SWI-Prolog, Extensions, Library, Top
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@node SWI-Prolog, SWI-Prolog Global Variables, Library, Top
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@cindex SWI-Prolog
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@menu SWI-Prolog Emulation
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Subnodes of SWI-Prolog
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* Invoking Predicates on all Members of a List :: maplist and friends
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* Forall :: forall built-in
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* hProlog and SWI-Prolog Attributed Variables :: Emulating SWI-like attributed variables
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* SWI-Prolog Global Variables :: Emulating SWI-like attributed variables
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@end menu
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@include swi.tex
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@node Extensions,Debugging,SWI-Prolog Global Variables,Top
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@chapter Extensions to Prolog
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YAP includes several extensions that are not enabled by
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default, but that can be used to extend the functionality of the
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system. These options can be set at compilation time by enabling the
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related compilation flag, as explained in the @code{Makefile}
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@menu
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Extensions to Traditional Prolog
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@ -12401,16 +12391,11 @@ no
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@cindex attributed variables
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@menu
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* Attribute Declarations:: Declaring New Attributes
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* Attribute Manipulation:: Setting and Reading Attributes
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* Attributed Unification:: Tuning the Unification Algorithm
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* Displaying Attributes:: Displaying Attributes in User-Readable Form
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* Projecting Attributes:: Obtaining the Attributes of Interest
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* Attribute Examples:: Two Simple Examples of how to use Attributes.
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* New Style Attribute Declarations:: New Style code
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* Old Style Attribute Declarations:: Old Style code (deprecated)
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@end menu
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YAP now supports the attributed variables packaged developed at OFAI by
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YAP supports attributed variables, originally developed at OFAI by
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Christian Holzbaur. Attributes are a means of declaring that an
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arbitrary term is a property for a variable. These properties can be
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updated during forward execution. Moreover, the unification algorithm is
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@ -12419,16 +12404,257 @@ trying to unify these variables.
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Attributed variables provide an elegant abstraction over which one can
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extend Prolog systems. Their main application so far has been in
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implementing constraint handlers, such as Holzbaur's CLPQR and Fruewirth
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and Holzbaur's CHR, but other applications have been proposed in the
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literature.
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implementing constraint handlers, such as Holzbaur's CLPQR, Fruewirth
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and Holzbaur's CHR, and CLP(BN).
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Different Prolog systems implement attributed variables in different
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ways. Traditionally, YAP has used the interface designed by SICStus
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Prolog. This interface is still
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available in the @t{atts} library, but from YAP-6.0.3 we recommend using
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the hProlog, SWI style interface. The main reason to do so is that
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most packages included in YAP that use attributed variables, such as CHR, CLP(FD), and CLP(QR),
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rely on the SWI-Prolog interface.
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The command
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@node New Style Attribute Declarations, Old Style Attribute Declarations, , Attributed Variables
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@section hProlog and SWI-Prolog style Attribute Declarations
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The following documentation is taken from the SWI-Prolog manual.
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Binding an attributed variable schedules a goal to be executed at the
|
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first possible opportunity. In the current implementation the hooks are
|
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executed immediately after a successful unification of the clause-head
|
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or successful completion of a foreign language (built-in) predicate. Each
|
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attribute is associated to a module and the hook @code{attr_unify_hook/2} is
|
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executed in this module. The example below realises a very simple and
|
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incomplete finite domain reasoner.
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|
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@example
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:- module(domain,
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[ domain/2 % Var, ?Domain
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]).
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:- use_module(library(ordsets)).
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domain(X, Dom) :-
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var(Dom), !,
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get_attr(X, domain, Dom).
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domain(X, List) :-
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list_to_ord_set(List, Domain),
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put_attr(Y, domain, Domain),
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X = Y.
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% An attributed variable with attribute value Domain has been
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% assigned the value Y
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attr_unify_hook(Domain, Y) :-
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( get_attr(Y, domain, Dom2)
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-> ord_intersection(Domain, Dom2, NewDomain),
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( NewDomain == []
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-> fail
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; NewDomain = [Value]
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-> Y = Value
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; put_attr(Y, domain, NewDomain)
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)
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; var(Y)
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-> put_attr( Y, domain, Domain )
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; ord_memberchk(Y, Domain)
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).
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% Translate attributes from this module to residual goals
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attribute_goals(X) -->
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@{ get_attr(X, domain, List) @},
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[domain(X, List)].
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@end example
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Before explaining the code we give some example queries:
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@multitable @columnfractions .70 .30
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@item @code{?- domain(X, [a,b]), X = c}
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@tab @code{fail}
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@item @code{domain(X, [a,b]), domain(X, [a,c]).}
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@tab @code{X=a}
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@item @code{domain(X, [a,b,c]), domain(X, [a,c]).}
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@tab @code{domain(X, [a,c]).}
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@end multitable
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The predicate @code{domain/2} fetches (first clause) or assigns
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(second clause) the variable a @emph{domain}, a set of values it can
|
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be unified with. In the second clause first associates the domain
|
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with a fresh variable and then unifies X to this variable to deal
|
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with the possibility that X already has a domain. The
|
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predicate @code{attr_unify_hook/2} is a hook called after a variable with
|
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a domain is assigned a value. In the simple case where the variable
|
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is bound to a concrete value we simply check whether this value is in
|
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the domain. Otherwise we take the intersection of the domains and either
|
||||
fail if the intersection is empty (first example), simply assign the
|
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value if there is only one value in the intersection (second example) or
|
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assign the intersection as the new domain of the variable (third
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example). The nonterminal @code{attribute_goals/3} is used to translate
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remaining attributes to user-readable goals that, when executed, reinstate
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these attributes.
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@table @code
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@item attvar(?@var{Term})
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@findex attvar/1
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@snindex attvar/1
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@cnindex attvar/1
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Succeeds if @code{Term} is an attributed variable. Note that @code{var/1} also
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succeeds on attributed variables. Attributed variables are created with
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@code{put_attr/3}.
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@item put_attr(+@var{Var},+@var{Module},+@var{Value})
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@findex put_attr/3
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@snindex put_attr/3
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||||
@cnindex put_attr/3
|
||||
|
||||
If @var{Var} is a variable or attributed variable, set the value for the
|
||||
attribute named @var{Module} to @var{Value}. If an attribute with this
|
||||
name is already associated with @var{Var}, the old value is replaced.
|
||||
Backtracking will restore the old value (i.e., an attribute is a mutable
|
||||
term. See also @code{setarg/3}). This predicate raises a representation error if
|
||||
@var{Var} is not a variable and a type error if @var{Module} is not an atom.
|
||||
|
||||
@item get_attr(+@var{Var},+@var{Module},-@var{Value})
|
||||
@findex get_attr/3
|
||||
@snindex get_attr/3
|
||||
@cnindex get_attr/3
|
||||
|
||||
Request the current @var{value} for the attribute named @var{Module}. If
|
||||
@var{Var} is not an attributed variable or the named attribute is not
|
||||
associated to @var{Var} this predicate fails silently. If @var{Module}
|
||||
is not an atom, a type error is raised.
|
||||
|
||||
@item del_attr(+@var{Var},+@var{Module})
|
||||
@findex del_attr/2
|
||||
@snindex del_attr/2
|
||||
@cnindex del_attr/2
|
||||
|
||||
Delete the named attribute. If @var{Var} loses its last attribute it
|
||||
is transformed back into a traditional Prolog variable. If @var{Module}
|
||||
is not an atom, a type error is raised. In all other cases this
|
||||
predicate succeeds regardless whether or not the named attribute is
|
||||
present.
|
||||
|
||||
@item attr_unify_hook(+@var{AttValue},+@var{VarValue})
|
||||
@findex attr_unify_hook/2
|
||||
@snindex attr_unify_hook/2
|
||||
@cnindex attr_unify_hook/2
|
||||
|
||||
Hook that must be defined in the module an attributed variable refers
|
||||
to. Is is called @emph{after} the attributed variable has been
|
||||
unified with a non-var term, possibly another attributed variable.
|
||||
@var{AttValue} is the attribute that was associated to the variable
|
||||
in this module and @var{VarValue} is the new value of the variable.
|
||||
Normally this predicate fails to veto binding the variable to
|
||||
@var{VarValue}, forcing backtracking to undo the binding. If
|
||||
@var{VarValue} is another attributed variable the hook often combines
|
||||
the two attribute and associates the combined attribute with
|
||||
@var{VarValue} using @code{put_attr/3}.
|
||||
|
||||
@item attr_portray_hook(+@var{AttValue},+@var{Var})
|
||||
@findex attr_portray_hook/2
|
||||
@snindex attr_portray_hook/2
|
||||
@cnindex attr_portray_hook/2
|
||||
|
||||
Called by @code{write_term/2} and friends for each attribute if the option
|
||||
@code{attributes(portray)} is in effect. If the hook succeeds the
|
||||
attribute is considered printed. Otherwise @code{Module = ...} is
|
||||
printed to indicate the existence of a variable.
|
||||
|
||||
@item attribute_goals(+@var{Var},-@var{Gs},+@var{GsRest})
|
||||
@findex attribute_goals/2
|
||||
@snindex attribute_goals/2
|
||||
@cnindex attribute_goals/2
|
||||
|
||||
This nonterminal, if it is defined in a module, is used by @var{copy_term/3}
|
||||
to project attributes of that module to residual goals. It is also
|
||||
used by the toplevel to obtain residual goals after executing a query.
|
||||
@end table
|
||||
|
||||
Normal user code should deal with @code{put_attr/3}, @code{get_attr/3} and @code{del_attr/2}.
|
||||
The routines in this section fetch or set the entire attribute list of a
|
||||
variables. Use of these predicates is anticipated to be restricted to
|
||||
printing and other special purpose operations.
|
||||
|
||||
@table @code
|
||||
|
||||
@item get_attrs(+@var{Var},-@var{Attributes})
|
||||
@findex get_attrs/2
|
||||
@snindex get_attrs/2
|
||||
@cnindex get_attrs/2
|
||||
|
||||
Get all attributes of @var{Var}. @var{Attributes} is a term of the form
|
||||
@code{att(@var{Module}, @var{Value}, @var{MoreAttributes})}, where @var{MoreAttributes} is
|
||||
@code{[]} for the last attribute.
|
||||
|
||||
@item put_attrs(+@var{Var},+@var{Attributes})
|
||||
@findex put_attrs/2
|
||||
@snindex put_attrs/2
|
||||
@cnindex put_attrs/2
|
||||
Set all attributes of @var{Var}. See @code{get_attrs/2} for a description of
|
||||
@var{Attributes}.
|
||||
|
||||
@item del_attrs(+@var{Var})
|
||||
@findex del_attrs/1
|
||||
@snindex del_attrs/1
|
||||
@cnindex del_attrs/1
|
||||
If @var{Var} is an attributed variable, delete @emph{all} its
|
||||
attributes. In all other cases, this predicate succeeds without
|
||||
side-effects.
|
||||
|
||||
@item term_attvars(+@var{Term},-@var{AttVars})
|
||||
@findex term_attvars/2
|
||||
@snindex term_attvars/2
|
||||
@cnindex term_attvars/2
|
||||
@var{AttVars} is a list of all attributed variables in @var{Term} and
|
||||
its attributes. I.e., @code{term_attvars/2} works recursively through
|
||||
attributes. This predicate is Cycle-safe.
|
||||
|
||||
@item copy_term(?@var{TI},-@var{TF},-@var{Goals})
|
||||
@findex copy_term/3
|
||||
@syindex copy_term/3
|
||||
@cnindex copy_term/3
|
||||
Term @var{TF} is a variant of the original term @var{TI}, such that for
|
||||
each variable @var{V} in the term @var{TI} there is a new variable @var{V'}
|
||||
in term @var{TF} without any attributes attached. Attributed
|
||||
variables are thus converted to standard variables. @var{Goals} is
|
||||
unified with a list that represents the attributes. The goal
|
||||
@code{maplist(call,@var{Goals})} can be called to recreate the
|
||||
attributes.
|
||||
|
||||
Before the actual copying, @code{copy_term/3} calls
|
||||
@code{attribute_goals/1} in the module where the attribute is
|
||||
defined.
|
||||
|
||||
@item copy_term_nat(?@var{TI},-@var{TF})
|
||||
@findex copy_term_nat/2
|
||||
@syindex copy_term_nat/2
|
||||
@cnindex copy_term_nat/2
|
||||
As @code{copy_term/2}. Attributes however, are @emph{not} copied but replaced
|
||||
by fresh variables.
|
||||
@end table
|
||||
|
||||
@node Old Style Attribute Declarations, , New Style Attribute Declarations, Attributed Variables
|
||||
@section SICStus Prolog style Attribute Declarations
|
||||
|
||||
@menu
|
||||
* Attribute Declarations:: Declaring New Attributes
|
||||
* Attribute Manipulation:: Setting and Reading Attributes
|
||||
* Attributed Unification:: Tuning the Unification Algorithm
|
||||
* Displaying Attributes:: Displaying Attributes in User-Readable Form
|
||||
* Projecting Attributes:: Obtaining the Attributes of Interest
|
||||
* Attribute Examples:: Two Simple Examples of how to use Attributes.
|
||||
@end menu
|
||||
|
||||
Old style attribute declarations are activated through loading the library @t{atts} . The command
|
||||
@example
|
||||
| ?- use_module(library(atts)).
|
||||
@end example
|
||||
enables the use of attributed variables. The package provides the
|
||||
enables this form of use of attributed variables. The package provides the
|
||||
following functionality:
|
||||
@itemize @bullet
|
||||
@item Each attribute must be declared first. Attributes are described by a functor
|
||||
@ -12453,8 +12679,8 @@ the top-level, where it is used to output the set of
|
||||
floundered constraints at the end of a query.
|
||||
@end itemize
|
||||
|
||||
@node Attribute Declarations, Attribute Manipulation, , Attributed Variables
|
||||
@section Attribute Declarations
|
||||
@node Attribute Declarations, Attribute Manipulation, , Old Style Attribute Declarations
|
||||
@subsection Attribute Declarations
|
||||
|
||||
Attributes are compound terms associated with a variable. Each attribute
|
||||
has a @emph{name} which is @emph{private} to the module in which the
|
||||
@ -12480,8 +12706,8 @@ preprocessed depending on the module. The @code{user:goal_expansion/3}
|
||||
mechanism is used for this purpose.
|
||||
|
||||
|
||||
@node Attribute Manipulation, Attributed Unification, Attribute Declarations, Attributed Variables
|
||||
@section Attribute Manipulation
|
||||
@node Attribute Manipulation, Attributed Unification, Attribute Declarations, Old Style Attribute Declarations
|
||||
@subsection Attribute Manipulation
|
||||
|
||||
|
||||
The attribute manipulation predicates always work as follows:
|
||||
@ -12531,8 +12757,8 @@ Remove the attribute with the same name. If no such attribute existed,
|
||||
simply succeed.
|
||||
@end table
|
||||
|
||||
@node Attributed Unification, Displaying Attributes, Attribute Manipulation, Attributed Variables
|
||||
@section Attributed Unification
|
||||
@node Attributed Unification, Displaying Attributes, Attribute Manipulation, Old Style Attribute Declarations
|
||||
@subsection Attributed Unification
|
||||
|
||||
The user-predicate predicate @code{verify_attributes/3} is called when
|
||||
attempting to unify an attributed variable which might have attributes
|
||||
@ -12569,8 +12795,8 @@ Succeed if @var{Var} is an attributed variable.
|
||||
|
||||
|
||||
|
||||
@node Displaying Attributes, Projecting Attributes,Attributed Unification, Attributed Variables
|
||||
@section Displaying Attributes
|
||||
@node Displaying Attributes, Projecting Attributes,Attributed Unification, Old Style Attribute Declarations
|
||||
@subsection Displaying Attributes
|
||||
|
||||
Attributes are usually presented as goals. The following routines are
|
||||
used by built-in predicates such as @code{call_residue/2} and by the
|
||||
@ -12594,8 +12820,8 @@ User-defined procedure, called to project the attributes in the query,
|
||||
|
||||
@end table
|
||||
|
||||
@node Projecting Attributes, Attribute Examples, Displaying Attributes, Attributed Variables
|
||||
@section Projecting Attributes
|
||||
@node Projecting Attributes, Attribute Examples, Displaying Attributes, Old Style Attribute Declarations
|
||||
@subsection Projecting Attributes
|
||||
|
||||
Constraint solvers must be able to project a set of constraints to a set
|
||||
of variables. This is useful when displaying the solution to a goal, but
|
||||
@ -12626,8 +12852,8 @@ original constraints into a set of new constraints on the projection,
|
||||
and these constraints are the ones that will have an
|
||||
@code{attribute_goal/2} handler.
|
||||
|
||||
@node Attribute Examples, ,Projecting Attributes, Attributed Variables
|
||||
@section Attribute Examples
|
||||
@node Attribute Examples, ,Projecting Attributes, Old Style Attribute Declarations
|
||||
@subsection Attribute Examples
|
||||
|
||||
The following two examples example is taken from the SICStus Prolog manual. It
|
||||
sketches the implementation of a simple finite domain ``solver''. Note
|
||||
|
||||
Reference in New Issue
Block a user