Class 34: Script-Fu Basics

Held Wednesday, April 4, 2001

Summary

Today we begin our investigations of Script-Fu, the Scheme-like language used for programming the GIMP.

Notes

• Are there questions on homework 5?
  • A few of you have asked about the sum we did in class. We did that version of sum on the first day we studied recursion. The key idea was that we used a helper function that took an extra parameter that kept track of the sum of the first k numbers in the list. You can see a newer version of the code (that uses all the clever design tricks we've learned) in sum.ss
  • Many of you were stumped by the intersection problem (number 6). My first solution used the rule that A intersect B is A-(A-B). Mr. Stone suggested that he was looking for a more elegant solution and indicated that complement would be useful. For a predicate, p, complement returns the "opposite" predicate (one that returns false when p returns true and vice versa). Here's a definition sans comment

    (define complement
      (lambda (pred?)
        (lambda (val) (not (pred? val)))))
    

• Here are some potentially useful links for your exploration of GIMP and Script-Fu
  • GIMP User's Manual
  • Mike Terry's Black Belt School of Script-Fu (more on Scheme than Script-Fu, but seems to be the primary reference)

Overview