Class 37: Pause for Breath

Held Friday, November 8, 2002

Summary

Today we pause for a moment to discuss problematic issues.

Assignments

• Exam 2: Higher-Order Scheme.
• Read Tail Recursion.

Notes

• Reminder: I'm happy to set up regular tutoring sessions (with me or with a tutor) for anyone who feels like he or she is having trouble with the material.
• Reminder: If you don't finish labs during class time, you should think about finishing them later. In this context, think about means: Either finish or be confident that you can.
• Comment on working together: The appropriate way to work together on an assignment is not You do problem 1, I do problem 2, you do problem 3, ....
  • Your results are not consistent.
  • You don't learn from the problems you don't do.
• Here are some of my experiments with the merge-images homework.

Overview

• Exam 2 distribution
• Recent questions and problems
• Files lab, continued

Exam 2

• Make sure to read the preliminaries.
• Discussion of the problems.

Questions and Answers

• make-tallier
  • It's probably useful to make a local helper procedure (the thing you return) rather than a separate tally.
• left-insert
  • No, (apply binproc lst) is not the answer I was looking for. Consider

    (define strange
      (lambda (x y)
        (+ (* 10 x) y)))
    (left-insert strange (list 4 3 2 1 6))
    

  • It's important to get the order of the parameters correct.
• read-lines
  • Two ways to use sample code: as a model and as a procedure you call.
  • You should use read-line as the latter.
  • General strategy: read each line from the file until you reach the end of the file.
  • Problem: How do you know when you're reached the end of the file?

Files Lab, Continued

• If there's any time left, you should continue to work on the files lab.