Jan Burse, created Sep 15. 2018
* Lexical comparison allows comparing terms without an attempt to
* instantiate the terms. These predicates are therefore meta-logical.
* The predicates (==)/2 and (\==)/2 perform an equality test. The
* predicates (@<)/2, (@=<)/2, (@>)/2 and (@>=)/2 use a linear ordering
* based on a lexical comparison. The lexical comparison first looks
* on the basic type of the involved terms. The ordering of the basic
* types is as follows:
* variable < decimal < float < integer < reference < atom < compound
* Variables are ordered according to their internal instantiation
* numbering. Integers, floats and decimals are arithmetically ordered.
* But there is no mixing of integers, floats and decimals. Atoms are
* ordered according to their internal character representation. For
* compounds first the arity is compared, then the functor is compared
* and finally the arguments from left to right. The predicate
* compare/3 returns <, = or >.
* ?- 1 @< 2.0.
* ?- compare(O, 1, 2.0).
* O = >
* Reference types can always be used in equality tests. Whether a
* reference type can be compared depends on whether it implements the
* Java Comparable interface. The predicates locale_compare/[3,4]
* allow a locale comparison. In locale comparison the atoms and
* functors are ordered according to a locale specific Java collator.
* Locale comparison for reference types is not yet supported.
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* X == Y: [ISO 8.4.1]
* The predicate succeeds when X is lexically equal to Y.
% +Term == +Term
* X \== Y: [ISO 8.4.1]
* The predicate succeeds when X is not lexically equal to Y.
% +Term \== +Term
* X @< Y: [ISO 8.4.1]
* The predicate succeeds when X is lexically before Y.
% +Term @< +Term
* X @=< Y: [ISO 8.4.1]
* The predicate succeeds when X is lexically before or equal to Y.
% +Term @=< +Term
* X @> Y: [ISO 8.4.1]
* The predicate succeeds when X is lexically after Y.
% +Term @> +Term
* X @>= Y: [ISO 8.4.1]
* The predicate succeeds when X is lexically after or equal to Y.
% +Term @>= +Term
* compare(O, X, Y): [TC2 8.4.2]
* The predicate succeeds when O unifies with the result of comparing
* X to Y. The result is one of the following atoms <, = or >.
% compare(-Atom, +Term, +Term)
* locale_compare(O, X, Y):
* locale_compare(C, O, X, Y):
* The predicate succeeds when O unifies with the result of locale
* comparing X to Y. The result is one of the following atoms <, =
* or >. The quaternary predicate allows specifying a locale C.
% locale_compare(-Atom, +Term, +Term)
% locale_compare(+Atom, -Atom, +Term, +Term)
locale_compare/4, 'SpecialLexical', 7).