These predicates implement "association list" primitives. They
use a binary tree representation. Thus the time complexity for these
predicates is O(lg N), where N is the number of keys.
These predicates also illustrate the use of compare/3
(see Term Compare) for case analysis.
The goal get_assoc(
Key,
Assoc,
Value)
is
true when Key is identical to one of the keys in Assoc, and
Value unifies with the associated value.
get_assoc(Key, t(K,V,L,R), Val) :- compare(Rel, Key, K), get_assoc(Rel, Key, V, L, R, Val). get_assoc(=, _, Val, _, _, Val). get_assoc(<, Key, _, Tree, _, Val) :- get_assoc(Key, Tree, Val). get_assoc(>, Key, _, _, Tree, Val) :- get_assoc(Key, Tree, Val).