Jan Burse, created Aug 17. 2019
* Type testing allows checking terms for their type without an
* attempt to instantiate. These predicates are therefore meta-logical.
* The basic data types of the ISO Prolog core standard are variable,
* atom, integer, float and compound. The Jekejeke Prolog system adds to
* these data types the data types reference and decimal.
* ?- callable(p(X,Y)).
* ?- callable(1).
* We find elementary test predicates such as var/1, atom/1, integer/1,
* float/1 and compound/1. For the Jekejeke Prolog specific data types
* we find the test predicates reference/1, decimal/1 float32/1 and
* float64/1. We find also test predicates that group different data
* types together such as nonvar/1, atomic/1, number/1 and callable/1.
* Warranty & Liability
* To the extent permitted by applicable law and unless explicitly
* otherwise agreed upon, XLOG Technologies GmbH makes no warranties
* regarding the provided information. XLOG Technologies GmbH assumes
* no liability that any problems might be solved with the information
* provided by XLOG Technologies GmbH.
* Rights & License
* All industrial property rights regarding the information - copyright
* and patent rights in particular - are the sole property of XLOG
* Technologies GmbH. If the company was not the originator of some
* excerpts, XLOG Technologies GmbH has at least obtained the right to
* reproduce, change and translate the information.
* Reproduction is restricted to the whole unaltered document. Reproduction
* of the information is only allowed for non-commercial uses. Selling,
* giving away or letting of the execution of the library is prohibited.
* The library can be distributed as part of your applications and libraries
* for execution provided this comment remains unchanged.
* Only to be distributed with programs that add significant and primary
* functionality to the library. Not to be distributed with additional
* software intended to replace any components of the library.
* Jekejeke is a registered trademark of XLOG Technologies GmbH.
* integer(X): [ISO 8.3.3]
* The predicate succeeds when X is an integer.
* float(X): [ISO 8.3.4]
* The predicate succeeds when X is a float.
* atom(X): [ISO 8.3.2]
* The predicate succeeds when X is an atom.
* compound(X): [ISO 8.3.6]
* The predicate succeeds when X is a compound.
* The predicate succeeds when X is a reference.
* The predicate succeeds when X is a decimal.
* number(X): [ISO 8.3.8]
* The predicate succeeds when X is a number, i.e. an integer, a float or a decimal.
* callable(X): [TC2 8.3.9]
* The predicate succeeds when X is callable, i.e. an atom or a compound.
* atomic(X): [ISO 8.3.5]
* The predicate succeeds when X is a constant, i.e. an atom, a number
* or a reference.
* var(X): [ISO 8.3.1]
* The predicate succeeds when X is a variable.
% already defined in member
* nonvar(X): [ISO 8.3.7]
* The predicate succeeds when X is not a variable, i.e. atomic or compound.
% already defined in member
* The predicate succeeds when X is a float32.
* The predicate succeeds when X is a float64.