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add_attribute(?Var, ?Attribute)
Add dynamically an attribute to a variable.
- ?Var
- Any term.
- ?Attribute
- Any term.
Description
The main use of this predicate is for dynamic attributed variables
creation. Since the number of declared extensions can vary with time,
attributes explicitly occurring in the source of extensions might be
created with less slots than currently necessary. To make sure that a
newly created attributed variable will have as many slots as necessary,
this predicate should be preferred to the equivalent
Var = _{Attribute}
If Var is a free variable, it will be bound to a new attributed variable
whose attribute corresponding to the caller module name will be
Attribute. If Var is already an attributed variable and the
corresponding attribute is a free variable, it will be bound to
Attribute. Otherwise, if the attribute is not a free variable or if Var
is instantiated, it will be unified with a new attributed variable whose
corresponding attribute is Attribute and all other attributes are free
variables.
Use add_attribute/3 to add an explicitly named attribute.
Fail Conditions
Fails if Var is not a free variable and its unification with the new
attributed variable fails.
Resatisfiable
No.
Exceptions
- (270) undefined variable attribute
- There is no attribute declared in the caller module.
Examples
[eclipse 6]: meta_attribute(eclipse, []).
yes.
[eclipse 3]: add_attribute(X, a), printf("%QPMw", X).
X{suspend : _g270 , a}
X = X
yes
See Also
meta_attribute / 2, add_attribute / 3