position-if predicate sequence &key from-end start end key    position

position-if-not predicate sequence &key from-end start end key    position

sequence - a proper sequence.

predicate - a designator for a function of one argument that returns a generalized boolean.

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.

start, end - bounding index designators of sequence. The defaults for start and end are 0 and nil, respectively.

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

position - a bounding index of sequence, or nil.

The position returned is the index within sequence of the rightmost (if from-end is true [see correction note below]) or of the leftmost (if from-end is false) element that satisfies the test; otherwise nil is returned. The index returned is relative to the left-hand end of the entire sequence, regardless of the value of start, end, or from-end.

 (position #\a "baobab" :from-end t)  4
 (position-if #'oddp '((1) (2) (3) (4)) :start 1 :key #'car)  2
 (position 595 '())   NIL
 (position-if-not #'integerp '(1 2 3 4 5.0))  4 

The function position-if-not is deprecated.