In a slideshow package such as powerpoint, overlays let the presenter add details to the slide that's already on the screen. This is useful when showing several steps in a single example, where each step builds on the previous ones.
For this assignment, add overlays to the slideshow program with dynamic content. Start with the file from class, and modify it accordingly. You will need to modify the data definition for programs to allow someone to specify overlays, modify the talk program to use overlays, and modify the interpreter to process the overlays.
As an example, here's how a run of the program with overlays might look:
------------------------------ Title: Hand Evals in DrScheme Hand evaluation helps you learn how Scheme reduces programs to values ------------------------------ n ------------------------------ Title: Example 1 ------------------------------ n ------------------------------ Title: Example 1 1. (+ (* 2 3) 6) ------------------------------ n ------------------------------ Title: Example 1 1. (+ (* 2 3) 6) 2. (+ 6 6) ------------------------------ n ------------------------------ Title: Example 1 1. (+ (* 2 3) 6) 2. (+ 6 6) 3. 12 ------------------------------ n ------------------------------ Title: Summary: How to Hand Eval 1. Find the innermost expression 2. Evaluate one step 3. Repeat until have a value ------------------------------ n End of show
The example 1 slide sequence comes from one slide and 3 overlays. Also note:
How should overlays behave? Here are some assumptions you can and cannot make, and some clarifications based on myWPI postings:
You may assume that the title appears on the original slide and that overlays do not add titles.
Overlays may add more than one item to a pointlist or more than one string at a time. How much info an overlay adds is specified at the level of individual overlays.
You are free to modify the existing data definitions on this assignment. You shouldn't need to modify them a lot though. If you find you are making lots of edits, come check with one of us before proceeding.
If you are stuck, here are some hints to get you started. I urge you to think about the problem for a while before looking at the hints -- you'll develop better language development instincts that way.
Turn in a single file hwk4.ss (or hwk4.scm) containing all code and documentation for this assignment. Make sure that both students' names are in a comment at the top of the file.
Refer to the Laws of Homework when preparing your solutions.