position; position-if; position-if-not

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position, position-if, position-if-not (Function)

Syntax:

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

— Function: position-if predicate sequence &key from-end start end key → position

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

Arguments and Values:

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.

Description:

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.

Examples:

 (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

Exceptional Situations:

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

Notes:

The :test-not argument is deprecated.

The function position-if-not is deprecated.