Jan Burse, created Sep 15. 2018
* 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 precondition 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.
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* 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.