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
undefined:

?- 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 sufficiently normalized.

The following surrogate predicates are provided:

**ord_get(M, K, V):**- The predicate succeeds for the value V associated with K in the ordered map M.
**ord_put(M, K, V, N):**- The predicate succeeds for an ordered map N where the value V is associated with the key K and the other key values are associated as in the ordered map M.
**ord_remove(M, K, N):**- The predicate succeeds for an ordered map N where the key K has no value and the other key values are associated as in the ordered map M.