Groups > comp.lang.forth > #20422

Rotate sequence

From	"WJ" <w_a_x_man@yahoo.com>
Newsgroups	comp.lang.forth
Subject	Rotate sequence
Date	2013-03-08 01:37 +0000
Organization	NewsGuy - Unlimited Usenet $19.95
Message-ID	<khbfcu0gki@enews4.newsguy.com> (permalink)

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P19 (**) Rotate a list N places to the left.
    Examples:
    * (rotate '(a b c d e f g h) 3)
    (D E F G H A B C)
   
    * (rotate '(a b c d e f g h) -2)
    (G H A B C D E F)

Factor:

: rotate ( seq n -- seq )
  dup 0 < [ abs cut* ] [ cut ] if
  swap append
;

{ "a" "b" "c" "d" "e" } 2 rotate .
{ "c" "d" "e" "a" "b" }
{ "a" "b" "c" "d" "e" } -2 rotate .
{ "d" "e" "a" "b" "c" }

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Rotate sequence "WJ" <w_a_x_man@yahoo.com> - 2013-03-08 01:37 +0000
  Re: Rotate sequence "WJ" <w_a_x_man@yahoo.com> - 2013-07-07 03:20 +0000

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