Function: reverse

reverse is a function defined in fns.c.

Signature

(reverse SEQ)

Documentation

Return the reversed copy of list, vector, or string SEQ.

See also the function nreverse, which is used more often.

Other relevant functions are documented in the string group.

View in manual

Shortdoc

;; string
(reverse "foo")
    => "oof"

Aliases

string-reverse (obsolete since 25.1)

Source Code

// Defined in /usr/src/emacs/src/fns.c
{
  Lisp_Object new;

  if (NILP (seq))
    return Qnil;
  else if (CONSP (seq))
    {
      new = Qnil;
      FOR_EACH_TAIL (seq)
	new = Fcons (XCAR (seq), new);
      CHECK_LIST_END (seq, seq);
    }
  else if (VECTORP (seq))
    {
      ptrdiff_t i, size = ASIZE (seq);

      new = make_uninit_vector (size);
      for (i = 0; i < size; i++)
	ASET (new, i, AREF (seq, size - i - 1));
    }
  else if (BOOL_VECTOR_P (seq))
    {
      EMACS_INT nbits = bool_vector_size (seq);

      new = make_clear_bool_vector (nbits, true);
      for (ptrdiff_t i = 0; i < nbits; i++)
	if (bool_vector_bitref (seq, nbits - i - 1))
	  bool_vector_set (new, i, true);
    }
  else if (STRINGP (seq))
    {
      ptrdiff_t size = SCHARS (seq), bytes = SBYTES (seq);

      if (size == bytes)
	{
	  ptrdiff_t i;

	  new = make_uninit_string (size);
	  for (i = 0; i < size; i++)
	    SSET (new, i, SREF (seq, size - i - 1));
	}
      else
	{
	  unsigned char *p, *q;

	  new = make_uninit_multibyte_string (size, bytes);
	  p = SDATA (seq), q = SDATA (new) + bytes;
	  while (q > SDATA (new))
	    {
	      int len, ch = string_char_and_length (p, &len);
	      p += len, q -= len;
	      CHAR_STRING (ch, q);
	    }
	}
    }
  else
    wrong_type_argument (Qsequencep, seq);
  return new;
}