Apropos

reverse, nreverseFunction

    Syntax

    reverse sequence reversed-sequence

    nreverse sequence reversed-sequence

    Arguments and Values

    sequence — a proper sequence.

    reversed-sequence — a sequence.

    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
    (setq str "abc")  "abc" 
    (reverse str)  "cba" 
    str  "abc" 
    (setq str (copy-seq str))  "abc" 
    (nreverse str)  "cba" 
    str  implementation-dependent 
    (setq l (list 1 2 3))  (1 2 3) 
    (nreverse l)  (3 2 1) 
    l  implementation-dependent
    Side Effects

    nreverse might either create a new sequence, modify the argument sequence, or both. (reverse does not modify sequence.)

    Exceptional Situations

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