diff options
Diffstat (limited to 'txr.1')
| -rw-r--r-- | txr.1 | 41 |
1 files changed, 36 insertions, 5 deletions
@@ -7869,7 +7869,7 @@ cached inside <promise> and returned, becoming the return value of the force function call. If the force function is invoked additional times on the same promise, the cached value is retrieved. -.SS Function perm +.SS Function rperm .TP Syntax: @@ -7884,16 +7884,21 @@ permutations of length <len> formed by items taken from <seq>. "Repeating" means that the items from <seq> can appear more than once in the permutations. -Argument <len> must be a positive integer, and <seq> must be a sequence. +The permutations which are returned are sequences of the same kind as <seq>. + +Argument <len> must be a nonnegative integer, and <seq> must be a sequence. -If <seq> is empty, or if <len> is zero, then the empty list is returned. +If <len> is zero, then a single permutation is returned, of zero length. +This is true regardless of whether <seq> is itself empty. -Otherwise permutations are returned which are sequences of the same kind as -<seq>. +If <seq> is empty and <len> is greater than zero, then no permutations are +returned, since permutations of a positive length require items, and the +sequence has no items. Thus there exist no such permutations. The first permutation consists of <len> repetitions of the first element of <seq>. The next repetition, if there is one, differs from the first repetition in that its last element is the second element of <seq>. +That is to say, the permutations are lexicographically ordered. .TP Examples: @@ -7904,6 +7909,32 @@ Examples: (rperm '(0 1 2) 2) -> ((0 0) (0 1) (0 2) (1 0) (1 1) (1 2) (2 0) (2 1) (2 2)) +.SS Function perm + +.TP +Syntax: + + (perm <seq> [<len>]) + +.TP +Description: + +The rperm function returns a lazy list which consists of all +length <len> permutations of formed by items taken from <seq>. +The permutations do not use any element of <seq> more than once. + +Argument <len>, if present, must be a positive integer no greater +than the length of <seq>, and <seq> must be a sequence. + +If <len> is not present, then its value defaults to the length of <seq>: +the list of the full permutations of the entire sequence is returned. + +The permutations in the returned list are sequences of the same kind as <seq>. + +If <len> is zero, then a list containing one permutation is returned, and that +permutations is of zero length. + +The permutations are lexicographically ordered. .SH CHARACTERS AND STRINGS |