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compare(?Ordering, ?Term1, ?Term2)

Succeeds if Ordering is a special atom which describes the ordering between Term1 and Term2.
?Ordering
Unifiable to a special atom describing the ordering between Term1 and Term2.
?Term1
An arbitrary term.
?Term2
An arbitrary term.

Description

Succeeds if Ordering is one of the special atoms ('<', '>' or '=') describing the standard ordering between the terms Term1 and Term2:

Ordering is the atom '<' iff Term1 comes before Term2 in the standard ordering.

Ordering is the atom '>' iff Term1 comes after Term2 in the standard ordering.

Ordering is the atom '=' iff Term1 is identical to Term2.

The standard ordering of ECLiPSe terms is defined as the following increasing order:

variables
(comparing two free variables yields an implementation-dependent and not necessarily reproducible result).
bounded reals
in ascending order (if bounds overlap, the order is by increasing lower bounds, then increasing upper bounds; if both bounds are the same, the two terms are considered equal).
floats
in ascending order.
rationals
in ascending order.
integers
in ascending order.
strings
lexicographical (ASCII) order
atoms
lexicographical (ASCII) order
compound terms
first by arity, then by functor name, then by the arguments in left to right order.

Fail Conditions

Fails if Ordering does not match the standard ordering between Term1 and Term2.

Resatisfiable

No.

Examples

   Success:
   compare(X, A, a), X = '<'.
   compare(X, a, A), X = '>'.
   compare('<', a(1,2), b(1,2)).
   compare(X, 1, 1), X = '='.
   compare(X, f(1), f(1)), X = '='.
   compare('<', 3.0, 2).
   compare('>', [a,b], [a|b]).
   compare('>', [a,b], [a|X]).
   Fail:
   compare('<', atomb, atoma).
   compare('=', 0, 1).
   compare('>',1.0,1).

See Also

@> / 2, @< / 2, @=< / 2, @>= / 2