#!/usr/bin/ucblogo

;; Copyright 2012 Kevin Ryde
;;
;; This file is part of Math-PlanePath.
;;
;; Math-PlanePath is free software; you can redistribute it and/or modify it
;; under the terms of the GNU General Public License as published by the Free
;; Software Foundation; either version 3, or (at your option) any later
;; version.
;;
;; Math-PlanePath is distributed in the hope that it will be useful, but
;; WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
;; or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
;; for more details.
;;
;; You should have received a copy of the GNU General Public License along
;; with Math-PlanePath.  If not, see <http://www.gnu.org/licenses/>.


;; cf A156595 xor adjacent mephisto waltz
;; 

;;-----------------------------------------------------------------------------

to increment :var
  make :var (thing :var)+1
end

to count.ternary.twos :n
  localmake "count 0
  while [:n <> 0] [
     if [(remainder :n 3) = 2] [increment "count];
     make "n int(:n/3)
  ]
  output :count
end

to mephisto.turn.angle :n
  output ifelse ((modulo (count.ternary.twos :n) 2) = 0) [60] [-60]
end

to mephisto :steps
  right 90
  left 45
  penup
  back 300
  right 90
  pendown

  localmake "step.len 3
  for [i 0 :steps 1] [
     forward :step.len
     left    mephisto.turn.angle :i
  ]
end

mephisto 2000