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.