This module provides ordered maps. The ordered maps are
represented by lists of key value pairs [k1-v1, .., kn-vn]. The
lists need to be key ordered and key duplicate free. If this
precondi-tion is violated the behaviour of the predicates is
?- ord_get([1-a,2-b], 2, X).
X = b
?- ord_put([1-a,2-b], 2, c, X).
X = [1-a,2-c]
The realization uses a membership check based on (==)/2 and lexical ordering based on (@<)/2. As a result the predicates are safe to be used with non-ground terms. On the other hand, since this comparison is not arithmetical, 1 and 1.0 are for example considered different.
An unordered map can be converted into an ordered map by using
the ISO predicate keysort/2. Also there is no need for predicate
permutation/2 here, since equality of ordered maps can be tested
via the ISO predicate ==/2, provided the keys and values are
The following surrogate predicates are provided: