documents/userman/extmeta.tex

9 % Software distributed under the License is distributed on an "AS IS"
38 for an object-level program, a metaterm looks like a variable, but for
47 In most situations an attributed variable behaves like a normal
53 \item an attributed variable has a number of associated \emph{attributes};
55 \item when an attributed variable occurs in the unification and in some
63 Before an attribute can be created and used, it must be declared
70 \about{Name} is an atom denoting the attribute name
103 all occurrences of an attributed variable in the source module may use the
149 If \about{Var} is already an attributed variable and its attribute is
157 The attributes of an attributed variable can be accessed using one-way
166 This clause succeeds only when the first argument is an attributed variable,
171 an attributed variable (it would create a new attributed variable and unify this
173 argument, but the unification is handled by an attributed variable handler, see
177 Often an extension must modify the data stored in the
206 modify the attribute or a part of it, so that an explicit
221 whenever an attributed variable occurs in one of the predefined
235 If \about{Name} is an existing extension, the specified handlers
238 Whenever one of the specified operations detects an attributed variable,
246 For instance, if an attributed variable \notation{X\{a:_, b:_, c:f(a)\}}
284 If an attributed variable is unified with a standard variable, the variable is
287 If an attributed variable is unified with another attributed variable or a
339 an attributed variable, they might not have the particular attribute that
341 correctly deal with all combinations of an attributed (but potentially
357 an attributed variable, the handler must check if \about{Copy} is still
358 a free variable or if it was already bound to an attributed variable by a
370 \about{AttrVar} is an attributed variable. The handler should bind
448 If no handler is specified for an attribute, or the print handler fails,
484 term, \about{GoalList} is an open-ended list of all delayed
547 This type-checking predicate succeeds iff its argument is an
548 ordinary free variable, it fails if it is an attributed variable.
551 This type-checking predicate succeeds iff its argument is an attributed
553 For other type testing predicates an attributed variable behaves like a
559 As an example, let us implement variables of enumerable types
670 A matching clause is the only way to decompose an attributed variable.
671 Note that this clause matches only calls that have an attributed variable