6.821 Class Weblog

I’ve posted solutions to all the problem sets so far, on the course website.  I’ll be adding PDF versions in the next couple of hours.  Please let me know, if you have any other questions.

Tuesday office hours are normally 3pm-4:30pm.

Today, however, they are moved forward 30 minutes, to run from 2:30pm-4pm, since I have a meeting I need to attend at 4pm.

The midterm has been postponed, 1 week, until Nov. 1st.

Let me know, if you have any questions.

I’ve put up four new sets of class notes, of my own typing, from Lectures #5-#8:

Lecture #5: The Language FL
Lecture #6: FL Semantics
Lecture #7: Parameter Passing & Scoping
Lecture #8: Non-Hierarchical Scoping & Object-Oriented Programming

Let me know if you have any questions.

Don’t forget — today Problem Set #2 is due at 1pm (unless you’ve been previously granted an extension).

Problem Set #3 will be handed out in class today.

See you all in an hour!

I’ve added a page to the course website, with a list of Errata that have been found so far for the Course Text.

If you are going to mail in a bug-report, please check this first to make sure it hasn’t already been discovered.

It would appear that the solution to PS #2’s problem 2(b) was accidentally added to the course text: notice that there’s a denotational semantics for EL given on page 122.

Yes, so — no need to do problem 2(b), then.

If you turn in an answer for that question anyway, and that answer conflicts with the book (and is correct), then that’ll probably count as a bug report.

And please, if you notice any more problem set questions that seem to be answered in the text, let me know.

Some of the sharp-eyed people who attended today’s recitation section may have noticed that, towards the end of the hour, I made a rather egregious error on the board.

I was trying to draw a Venn diagram that would show the relationship between continuous and monotonic functions.

I should have consulted the text because, in my haste, I got the figure wrong on the board. I drew the set of the set of continuous functions as being ‘larger’ than the set of monotonic functions, but it should be the other way around: if a function is continuous, then it is also monotonic. (This is true when the domain and range of the function are both CPOs.)

This is outlined on pages 175 and 176 of the course-text, which I strongly recommend everyone re-read.

It’s important to get this detail right, since the proof of the existence of a fixed-point when iterating a continuous generating function on the bottom element relies on the sequence of iterated values being a chain (which itself relies on the function being monotonic — so montonicity had better follow from continuity).

I hope that didn’t confuse anyone too badly.

My personal notes for lecture 4 have now been posted.

Lecture #4: Fixed Points

And a reminder: I’ll be discussing all of this, including working an example of the fixed point operator, in the recitation section at 11am tomorrow.

First, a reminder: Problem Set #1 Part B is due today.  Please make sure you’ve turned it in to me, in some form, by 1pm this afternoon.

Next, a note: Problem Set #2 will be distributed today.  Solutions for Problem Set #1 Part B won’t be distributed  until Thursday, however, since several students have been granted extensions.

See you all in class!