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mismatch (Function)

— Function: mismatch sequence-1 sequence-2 &key from-end test test-not key start1 start2 end1 end2 position
Arguments and Values:

Sequence-1—a sequence.

Sequence-2—a sequence.

from-end—a generalized boolean. The default is false.

test—a designator for a function of two arguments that returns a generalized boolean.

test-not—a designator for a function of two arguments that returns a generalized boolean.

start1, end1bounding index designators of sequence-1. The defaults for start1 and end1 are 0 and nil, respectively.

start2, end2bounding index designators of sequence-2. The defaults for start2 and end2 are 0 and nil, respectively.

key—a designator for a function of one argument, or nil.

position—a bounding index of sequence-1, or nil.


The specified subsequences of sequence-1 and sequence-2 are compared element-wise.

The key argument is used for both the sequence-1 and the sequence-2.

If sequence-1 and sequence-2 are of equal length and match in every element, the result is false. Otherwise, the result is a non-negative integer, the index within sequence-1 of the leftmost or rightmost position, depending on from-end, at which the two subsequences fail to match. If one subsequence is shorter than and a matching prefix of the other, the result is the index relative to sequence-1 beyond the last position tested.

If from-end is true, then one plus the index of the rightmost position in which the sequences differ is returned. In effect, the subsequences are aligned at their right-hand ends; then, the last elements are compared, the penultimate elements, and so on. The index returned is an index relative to sequence-1.

 (mismatch "abcd" "ABCDE" :test #'char-equal)  4
 (mismatch '(3 2 1 1 2 3) '(1 2 3) :from-end t)  3
 (mismatch '(1 2 3) '(2 3 4) :test-not #'eq :key #'oddp)  NIL
 (mismatch '(1 2 3 4 5 6) '(3 4 5 6 7) :start1 2 :end2 4)  NIL
See Also:

Section 3.6 (Traversal Rules and Side Effects)


The :test-not argument is deprecated.