[ Predicate Database and Compiler | Reference Manual | Alphabetic Index ]
Specifies the meta-arguments for the given predicates
- Callable term with meta-argument indicators, or a comma-separated list of such.
This declaration is normally used as a directive in compiled code,
to specify if and how the arguments of a predicate refer to other
predicates (meta-arguments). In ECLiPSe 6.1, this declaration does
not affect the semantics of the program, and is only used by
development tools like the cross-referencer or coverage analyser.
In future releases, the compiler may make use of the information.
The meta-argument indicators describes the control flow through the
arguments of a meta-predicate. The functor and arity of MetaSpec
correspond to the functor and arity of the meta-predicate. The arguments
are each populated with one of the following atomic descriptors:
Instead of the '*', which marks a non-meta argument, a mode indicator
can be given. The effect is the same as specifying '*', and giving
the mode in a separate mode/1 declaration:
A goal that is called as a subgoal of the declared predicate.
A positive integer
A subgoal is constructed by appending the number of specified
arguments, and then called.
A clause (a fact or a rule).
A PredSpec of the form Name/Arity.
A module-sensitive argument, but none of the above.
An argument that is not one of the above.
The argument is instantiated, i.e. it is not a variable.
The argument is ground, i.e. contains no variables.
The argument is not instantiated, it must be a free variable without
any constraints or aliases.
The mode is not known or it is neither of the above.
If one of the declared predicates does not exist, a local undefined
predicate is created.
The declared meta-predicate information can be accessed by retrieving
the predicate's 'meta_predicate' and 'mode' properties with get_flag/3.
Modes and Determinism
- meta_predicate(++) is det
This predicate is sensitive to its module context (tool predicate, see @/2).
- (4) instantiation fault
- MetaSpecs is not ground
- (5) type error
- MetaSpecs is not a callable term, or a comma list of such
- (6) out of range
- The callable term arguments are not meta-argument indicators
:- meta_predicate p(:,*,*).
:- meta_predicate q(0,+,-).
compile / 1, get_flag / 3, mode / 1, library(instrument), library(xref), library(coverage), library(lint)