Comparing terms

Author(s): Daniel Cabeza, Manuel Hermenegildo.

Version: 1.5#118 (2000/4/19, 18:13:43 CEST)

These built-in predicates are extra-logical. They treat uninstantiated variables as objects with values which may be compared, and they never instantiate those variables. They should not be used when what you really want is arithmetic comparison or unification.

The predicates make reference to a standard total ordering of terms, which is as follows:

• Variables, by age (roughly, oldest first -- the order is not related to the names of variables).
• Floats, in numeric order (e.g. -1.0 is put before 1.0).
• Integers, in numeric order (e.g. -1 is put before 1).
• Atoms, in alphabetical (i.e. character code) order.
• Compound terms, ordered first by arity, then by the name of the principal functor, then by the arguments in left-to-right order. Recall that lists are equivalent to compound terms with principal functor '.'/2.

For example, here is a list of terms in standard order:

[ X, -1.0, -9, 1, bar, foo, [1], X = Y, foo(0,2), bar(1,1,1) ]

• Usage and interface (term_compare)
• Documentation on exports (term_compare)

Usage and interface (term_compare)

Documentation on exports (term_compare)

PROPERTY: ==/2:

Usage 1: Term1 == Term2

• Description: The terms Term1 and Term2 are strictly identical.
• The following properties should hold globally: Term1 is not further instantiated. (basic_props:not_further_inst/2) Term2 is not further instantiated. (basic_props:not_further_inst/2)

Usage 2: Term1 == Term2

• Description: The terms Term1 and Term2 are strictly identical.
• The following properties should hold globally: Term1 is not further instantiated. (basic_props:not_further_inst/2) Term2 is not further instantiated. (basic_props:not_further_inst/2)

PROPERTY: \==/2:

Usage 1: Term1 \== Term2

• Description: The terms Term1 and Term2 are not strictly identical.
• The following properties should hold globally: Term1 is not further instantiated. (basic_props:not_further_inst/2) Term2 is not further instantiated. (basic_props:not_further_inst/2)

Usage 2: Term1 \== Term2

• Description: The terms Term1 and Term2 are not strictly identical.
• The following properties should hold globally: Term1 is not further instantiated. (basic_props:not_further_inst/2) Term2 is not further instantiated. (basic_props:not_further_inst/2)

PROPERTY: @</2:

Usage 1: @<(Term1,Term2)

• Description: The term Term1 precedes the term Term2 in the standard order.
• The following properties should hold globally: Term1 is not further instantiated. (basic_props:not_further_inst/2) Term2 is not further instantiated. (basic_props:not_further_inst/2)

Usage 2: @<(Term1,Term2)

• Description: The term Term1 precedes the term Term2 in the standard order.
• The following properties should hold globally: Term1 is not further instantiated. (basic_props:not_further_inst/2) Term2 is not further instantiated. (basic_props:not_further_inst/2)

PROPERTY: @=</2:

Usage 1: @=<(Term1,Term2)

• Description: The term Term1 precedes or is identical to the term Term2 in the standard order.
• The following properties should hold globally: Term1 is not further instantiated. (basic_props:not_further_inst/2) Term2 is not further instantiated. (basic_props:not_further_inst/2)

Usage 2: @=<(Term1,Term2)

• Description: The term Term1 precedes or is identical to the term Term2 in the standard order.
• The following properties should hold globally: Term1 is not further instantiated. (basic_props:not_further_inst/2) Term2 is not further instantiated. (basic_props:not_further_inst/2)

PROPERTY: @>/2:

Usage 1: @>(Term1,Term2)

• Description: The term Term1 follows the term Term2 in the standard order.
• The following properties should hold globally: Term1 is not further instantiated. (basic_props:not_further_inst/2) Term2 is not further instantiated. (basic_props:not_further_inst/2)

Usage 2: @>(Term1,Term2)

• Description: The term Term1 follows the term Term2 in the standard order.
• The following properties should hold globally: Term1 is not further instantiated. (basic_props:not_further_inst/2) Term2 is not further instantiated. (basic_props:not_further_inst/2)

PROPERTY: @>=/2:

Usage 1: @>=(Term1,Term2)

• Description: The term Term1 follows or is identical to the term Term2 in the standard order.
• The following properties should hold globally: Term1 is not further instantiated. (basic_props:not_further_inst/2) Term2 is not further instantiated. (basic_props:not_further_inst/2)

Usage 2: @>=(Term1,Term2)

• Description: The term Term1 follows or is identical to the term Term2 in the standard order.
• The following properties should hold globally: Term1 is not further instantiated. (basic_props:not_further_inst/2) Term2 is not further instantiated. (basic_props:not_further_inst/2)

PREDICATE: compare/3:

compare(Op,Term1,Term2)

Op is the result of comparing the terms Term1 and Term2.

Usage 1: compare(?(atm),@(term),@(term))

• The following properties should hold upon exit: ?(atm) is an element of [=,>,<]. (basic_props:member/2) @(term) is any term. (basic_props:term/1) @(term) is any term. (basic_props:term/1)

Usage 2:

• Call and exit should be compatible with: Op is an atom. (basic_props:atm/1)
• The following properties should hold at call time: Term1 is any term. (basic_props:term/1) Term2 is any term. (basic_props:term/1)
• The following properties should hold upon exit: Op is an atom. (basic_props:atm/1) Term1 is any term. (basic_props:term/1) Term2 is any term. (basic_props:term/1) Op is an element of [=,>,<]. (basic_props:member/2) Term1 is any term. (basic_props:term/1) Term2 is any term. (basic_props:term/1)
• The following properties should hold globally: Term1 is not further instantiated. (basic_props:not_further_inst/2) Term2 is not further instantiated. (basic_props:not_further_inst/2)

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