anchor.diff:  
   (in-package :petalisp-getting-started)
   
  +;;; First of all, we define an auxiliary function PRESENT, that first shows
  +;;; the data flow representation of a Petalisp datum, then evaluates it and
  +;;; finally prints its value to the standard output.
   (defun present (expression)
     (petalisp-dev:view expression)
     (format t "~%=> ~A~%~%" (compute expression)))
  
positive.code:  (jacobi-2d
    (jacobi-2d domain)))
  
  
negative.code: ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;;;
  ;;; Petalisp Basics
  
  (present
   (reshape 0 '())) ; the empty space
  