
compare(-Ordering, ?Term1, ?Term2)

   Succeeds if Ordering is a special atom which describes the ordering between
Term1 and Term2.



Arguments
   Ordering            Unifiable to a special atom describing the ordering between                Term1 and Term2.
   Term1               An arbitrary term.
   Term2               An arbitrary term.

Type
   Comparing and Sorting

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, with negative zeros (-0.0) being different and
    before positive zeros (0.0).

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.


   Note in particular that numbers are first ordered by their type (integer,
   float, etc) and only then by their magnitude, i.e. when comparing numbers
   of different types, the result is not necessarily their numerical order.


Modes and Determinism
   compare(-, ?, ?) is det

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).              % not arithmetic order!
   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
