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meta_predicate(++MetaSpecs)
Specifies the meta-arguments for the given predicates
- MetaSpecs
- Callable term with meta-argument indicators, or a comma-separated list of such.
Description
   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:
    0
- 
	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.
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:
- 
    + 
- 
	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
Modules
This predicate is sensitive to its module context (tool predicate, see @/2).
Exceptions
- (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
Examples
:- meta_predicate p(:,*,*).
:- meta_predicate q(0,+,-).
:- meta_predicate
	maplist(2,*,*),
	checklist(1,*).
See Also
compile / 1, get_flag / 3, mode / 1, library(instrument), library(xref), library(coverage), library(lint)