
hash_update(+Table, ++Key, -OldValue, +NewValue)

   Lookup and replace the value stored under Key

Arguments
   Table               A hash table
   Key                 a ground term
   OldValue            Any term
   NewValue            Any term

Type
   library(hash)

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
