position item sequence &key from-end test test-not start end key → position

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

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

item — an object.

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.

position, position-if, and position-if-not each search sequence for an element that satisfies the test.

The position returned is the index within sequence of the leftmost (if from-end is true) or of the rightmost (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

Should be prepared to signal an error of type type-error if sequence is not a proper sequence.

find, Section 3.6 (Traversal Rules and Side Effects)

The :test-not argument is deprecated.

The function position-if-not is deprecated.