#!/home/arne/wisp/wisp-multiline.sh 
; !#

; A world projected on a d20 (20-sided die)

; For this we need a vector with 20 elements, a vector which shows the
; neighboring elements and accessor functions which give us the
; relevant elements for any set of longitude and latitude as well as
; its inverse (element-id to lon+lat). For further subdivisions, just
; elevate the center of each edge and connect these centers.

. (define world (make-vector 20))
. (define neighbors (make-vector 20))
; count from the top
; Contains the numbers instead of the indexes, to make it easier for
; me to think about them.
; 
;   7       8
;    3    4  
;       1        
;   6   2   9
;     5   10
; 
;    14       13
;     18    17
;        20        
;   15   19   12
;     16    11
; 
. (define neighbors-helper
  '((1 2 3 4)
    (2 1 5 10)
    (3 1 6 7)
    (4 1 8 9)
    (5 2 6 14)
    (6 3 5 15)
    (7 3 8 16)
    (8 4 7 11)
    (9 4 10 12)
    (10 1 9 13)
    (20 19 18 17)
    (19 20 16 11)
    (18 20 15 14)
    (17 20 13 12)
    (16 19 17 7)
    (15 18 16 6)
    (14 18 13 5)
    (13 17 14 10)
    (12 17 11 9)
    (11 19 12 8)))

. (let loop ((relationships neighbors-helper))
  (cond 
   ((null? relationships)
    neighbors)
   (else
    (let* ((cur (car relationships))
           (idx (1- (car cur)))
           (vec (cdr cur)))
      (vector-set! world idx idx)
      (vector-set! neighbors idx (make-vector 3))
      (let setidx ((idxtoset '(0 1 2)))
        (cond 
         ((null? idxtoset)
          #t)
         (else
          (vector-set!
           (vector-ref neighbors idx)
           (car idxtoset)
           (1- (list-ref vec (car idxtoset))))
          (setidx (cdr idxtoset)))))
      (loop (cdr relationships))))))
. (display world)
. (newline)
. (display neighbors)
. (newline)
. (display (vector-ref world 0))
. (newline)