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Function REVERSE, NREVERSE

Syntax

  • reverse sequencereversed-sequence
  • nreverse sequencereversed-sequence

Arguments and Values

Description

reverse and nreverse return a new sequence of the same kind as sequence, containing the same elements, but in reverse order.

reverse and nreverse differ in that reverse always creates and returns a new sequence, whereas nreverse might modify and return the given sequence. reverse never modifies the given sequence.

For reverse, if sequence is a vector, the result is a fresh simple array of rank one that has the same actual array element type as sequence. If sequence is a list, the result is a fresh list.

For nreverse, if sequence is a vector, the result is a vector that has the same actual array element type as sequence. If sequence is a list, the result is a list.

For nreverse, sequence might be destroyed and re-used to produce the result. The result might or might not be identical to sequence.

Specifically, when sequence is a list, nreverse is permitted to setf any part, car or cdr, of any cons that is part of the list structure of sequence. When sequence is a vector, nreverse is permitted to re-order the elements of sequence in order to produce the resulting vector.

Examples

(defparameter *str* "abc")

"abc"

(reverse *str*)

"cba"

*str*

"abc"

(defparameter *str* (copy-seq *str*))

"abc"

(nreverse *str*)

"cba"

*str*

implementation-dependent

(defparameter *list* (list 1 2 3))

(1 2 3)

(nreverse *list*)

(3 2 1)

*list*

implementation-dependent

Side Effects

nreverse might either create a new sequence, modify the argument sequence, or both.

(reverse does not modify sequence.)

Affected By

None.

Exceptional Situations

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

See Also

None.

Notes

None.

\issue{REMF-DESTRUCTION-UNSPECIFIED:X3J13-MAR-89}