Meta-properties

Author(s): Francisco Bueno.

This library allows the use of some meta-constructs which provide for specifying properties of terms which are unknown at the time of the specification, or expressed with a shorthand for the property definition, i.e., without really defining it.

An example of such use is an assertion which specifies that any property holding upon call will also hold upon exit:

         :- pred p(X) : Prop(X) => Prop(X).

Another example is using shorthands for properties when documenting:

         :- pred p(X) : regtype(X,(^(list;list);list)).

(See below for an explanation of such a regular type.)

• Usage and interface (meta_props)
• Documentation on exports (meta_props)
• Documentation on multifiles (meta_props)
• Documentation on internals (meta_props)
• Known bugs and planned improvements (meta_props)

Usage and interface (meta_props)

Documentation on exports (meta_props)

PROPERTY: call/2:

call(P,A)

A has property P (provided that P is a property). Equivalent to P(A).

Usage: call(P,A)

• Description: A has property P.
• If the following properties hold at call time: P is a term which represents a goal, i.e., an atom or a structure. (basic_props:callable/1)

PROPERTY: prop/2:

Usage: prop(A,P)

• Description: A has property P.
• If the following properties hold at call time: P has property ^ (callable;prop_abs). (meta_props:prop/2)

PROPERTY: regtype/2:

Usage: regtype(A,T)

• Description: A is of type T.
• If the following properties hold at call time: T has property ^ (regtype;prop_abs). (meta_props:prop/2)

Documentation on multifiles (meta_props)

PREDICATE: callme/2:

(User defined.) A hook predicate you have to define as callme(P,X):- P(X), !. in the program that uses this library. This is done automatically if the package is used instead of the library module (but then you should not define callme/2 in your program).

The predicate is multifile.

Documentation on internals (meta_props)

PROPERTY: prop_abs/1:

prop_abs(Prop)

Prop is a property abstraction, i.e., a parametric property, or a term formed of property abstractions, where the functors used in the term are escaped by ^.

One particular case of property abstractions are parametric regular type abstractions, i.e., a parametric type functor or a ^-escaped term formed of regular type abstractions.

Such abstractions are a short-hand for a corresponding regular type (correspondingly, property). For example, the following abstraction:

         ^(list;list);list

denotes terms of the form (X;Y) where list(X) and list(Y) hold and also terms T such that list(T) holds. It is equivalent to the regular type:

         abstract_type((X;Y)):- list(X), list(Y).
         abstract_type(T):- list(T).

Usage: prop_abs(Prop)

• Description: Prop is a property abstraction.

Known bugs and planned improvements (meta_props)

• Using a hook predicate is not very elegant. Need something else.
• The cut in the hook prevents backtracking (enough for most uses of properties but not quite ok).

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