; makes a world matrix
  (def makeworld (x)
    (= world (n-of x (n-of x nil))) ; world of nil
    (= merged (n-of x (n-of x nil))) ; layer of movers
    nil)


  ; print out the world, imposing a list of critters
  ; on top of it. The list itself assumes that its entries
  ; are tables which have a symbol and a position field
  (def show (lst)
    ; copy world into merged
    (for y 0 (- (len world) 1)
      (for x 0 (- (len world) 1)
        (= ((merged y) x) ((world y) x))))
    ; superimpose critters
    (each c lst
      (= ((merged (car (c "pos"))) (cadr (c "pos"))) (c "symbol")))
    ; plot world
    (each row merged
      (each pos row (if (is pos nil) (pr #\. #\space) (pr pos #\space)))
      (prn)))

  (= creature (table))
  (= creature2 (table))
  (= creature3 (table))
  (= (creature "pos") '(1 3))
  (= (creature2 "pos") '(10 3))
  (= (creature3 "pos") '(8 8))
  (= (creature "symbol") #\$)
  (= (creature2 "symbol") #\@)
  (= (creature3 "symbol") #\#)
  (makeworld 15)

  arc> (show (list creature creature2 creature3))
  . . . . . . . . . . . . . . . 
  . . . $ . . . . . . . . . . . 
  . . . . . . . . . . . . . . . 
  . . . . . . . . . . . . . . . 
  . . . . . . . . . . . . . . . 
  . . . . . . . . . . . . . . . 
  . . . . . . . . . . . . . . . 
  . . . . . . . . . . . . . . . 
  . . . . . . . . # . . . . . . 
  . . . . . . . . . . . . . . . 
  . . . @ . . . . . . . . . . . 
  . . . . . . . . . . . . . . . 
  . . . . . . . . . . . . . . . 
  . . . . . . . . . . . . . . . 
  . . . . . . . . . . . . . . . 
  nil

It's the start of a new project for me (and hopefully later on a postdoc position on the topic). The idea is to build some kind of smart animals in an artificial world, without having to design them, or run through countless of iterations with genetic algorithms to get one.