To get your participation credit, make sure you
upload your Definitions file to turnin before you leave the lab!
(This work will not be graded---full credit just for submitting.)
This lab is designed to give you more experience working with interpreters by having you extend the interpreter for slideshows.
You need to use Advanced Student language level for this lab!
Put your name in a comment at the top of the Definitions area.
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 lab, add overlays to the slideshow program. 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:
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Title: Hand Evals in DrRacket
Hand evaluation helps you learn how Racket reduces programs to values
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Title: Example 1
- (+ (* 2 3) 6)
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Title: Example 1
- (+ (* 2 3) 6)
- (+ 6 6)
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Title: Example 1
- (+ (* 2 3) 6)
- (+ 6 6)
- 12
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Title: Summary: How to Hand Eval
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Title: Summary: How to Hand Eval
1. Find the innermost expression
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Title: Summary: How to Hand Eval
1. Find the innermost expression
2. Evaluate one step
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Title: Summary: How to Hand Eval
1. Find the innermost expression
2. Evaluate one step
3. Repeat until have a value
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End of show
The example slide sequence above comes from one regular slide, followed by a slide with 2 overlays, followed by a slide with 3 overlays. Note that the overlays taken together seem to form one complete slide (e.g., if a numbered point list is broken into overlays, the numbering should be consistent).
How should overlays behave? Here are some simplifying assumptions for this exercise:
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 point list 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. You shouldn't need to modify them a lot though. If you find you are making lots of edits, ask for help.
Everyone should be able to extend the data definitions, modify the talk program to specify the above example, and figure out where to edit the interpreter to process the overlays.
Hint 1: Add a new type of slide (e.g., slide-with-overlays) that has a title, a body and a list of overlays. Initially allow only one overlay, get everything working, then extend the code to support an arbitrary number of overlays.
Hint 2: The existing print-slide function knows
how to handle regular slides (without overlays). Can you find a way
to reuse this function (without editing it) to display slides with
overlays? Consider making a temporary instance of a regular slide
using material from overlays.