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update(+Key, +Struct, +Old, -New)

Incorporate Struct into a duplicate-free sorted list
Key argument position (non-negative integer, or list of those)
Strictly ordered list of structures
Strictly ordered list of structures, or variable


Inserts the compound term Struct into the ordered list Old, giving New. The lists are both in strictly ascending order (according to their elements' Key'th argument), i.e. without duplicates. If Old already contains an element with the same key as Struct, then Struct replaces this existing element. Otherwise, Struct is inserted at the correct position to maintain the list order.

The list New is either of the same length as Old, or one longer.

Modes and Determinism


(4) instantiation fault
Arguments are insufficiently instantiated
(5) type error
Some argument or its components are of the wrong type
(6) out of range
Some structure does not have a Key'th argument


    ?- update(1, f(2,b), [f(1,a),f(3,c)], New).
    New = [f(1,a), f(2,b), f(3,c)]
    Yes (0.00s cpu)

    ?- update(1, f(2,new), [f(1,a),f(2,b),f(3,c)], New).
    New = [f(1,a), f(2,new), f(3,c)]
    Yes (0.00s cpu)

See Also

merge / 5, sort / 4