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hash_update(+Table, ++Key, -OldValue, +NewValue)
Lookup and replace the value stored under Key
- Table
- A hash table
- Key
- a ground term
- OldValue
- Any term
- NewValue
- Any term
Description
A combination of hash_get/3 and hash_set/3, but more efficient
    	because there is only one hash lookup.
Modes and Determinism
- hash_update(+, ++, -, +) is semidet
Fail Conditions
No entry for Key
Examples
	?- hash_create(H),
	   hash_set(H, k, hello),
	   hash_update(H, k, Old, world),
	   hash_get(H, k, New).
	Old = hello
	New = world
	Yes (0.00s cpu)
	% sample code based on hash_update/4:
    	hash_inc(H, Key) :-
	    hash_update(H, Key, N0, N1),
	    N1 is N0+1.
    	hash_addto(H, Key, Value) :-
	    hash_update(H, Key, Values, [Value|Values]).
    
See Also
hash_get / 3, hash_set / 3