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merge(+List1, +List2, ?List3)

Succeeds if List3 is a merged list of List1 and List2. If both lists are sorted, List3 will be sorted.
+List1
List.
+List2
List.
?List3
List or variable.

Description

Used to merge the sorted lists List1 and List2 to give the sorted list List3. merge(L1,L2,L3) is equivalent to merge(0,=<,L1,L2,L3).

For two lists [e1,e2,e3] and [f1,f2,f3], e1 is compared to f1. The lower (dictated by the standard ordering below) is put into List3, and the next element is compared to the next element in the other list. This process continues until both lists are exhausted.

In particular, this will merge two sorted lists into a sorted list.

The sort is done according to the standard ordering of terms. Duplicates are not removed. See compare/3 for this standard ordering.

Fail Conditions

Fails if List3 does not unify with the merging of the lists List1 and List2 outlined below.

Resatisfiable

No.

Examples

Success:
      merge([2,4,6],[1,3,5],L).
                            (gives L=[1,2,3,4,5,6]).
      merge([f(1),f(7)],[f(8),f(10)],L).
                          (gives L=[f(1),f(7),f(8),f(10)]).
      merge([f(5),f(8)],[f(1),f(2),f(2),f(5),f(8)],L).
            (gives L=[f(1),f(2),f(2),f(5),f(5),f(8),f(8)]).
      merge([a,w],[a,b,b,r,w],L).
            (gives L=[a,a,b,b,r,w,w]).
      merge([f(2),f(1)],[f(3),f(8)],L).
            (gives L=[f(2),f(1),f(3),f(8)]).

Fail:
      merge([2,4,6],[1,3,5],[1,2,3,4,5]).

See Also

compare / 3, merge / 5, msort / 2