[plt-scheme] Scheme projects in my undergrad CS course

From: Fred G. Martin (fredm at cs.uml.edu)
Date: Fri Jan 9 13:53:29 EST 2009

Hi everyone,

This is a belated reply to Eric Tanter and Shriram Krishnamurthi's
questions about how I structured student projects in my last
semester's junior-level PL course, which was based on Scheme and SICP.

This was the first time that students were required to do projects in
our undergrad PL course, and they were quite successful.  Since I
wrote last, I graded the projects.  Broadly, I'd categorize them as
1/3 excellent, 1/3 decent, and 1/3 weak (I suppose that's a normal
distribution of anything we do...).  But that's still 2/3 of students
really exercising ideas in Scheme and PLs (functional programming,
map/filter, recursion) for their own purposes, which I think could be
quite valuable in the long run.

from Eric:

> Can you tell us more about how the projects
> were conceived? did they all pop up out of students' mind, if so,
> under which guidelines if any? or did you have a pool of project ideas?

I started out by telling them about the project on the first class
meeting, letting students know that the project would be worth 25% of
their overall grade (the final exam was only worth 20%!).  Here's what
I wrote in the syllabus:

"In the final project, you will apply the ideas developed in the class
in an original software implementation. You may thus connect the ideas
of the class with your own interests—music, robotics, art, databases,
the web, networking, gaming, etc. The learning goal of the project is
to have you find some real-world relevance of the ideas in the class."

Then, during the semester, I showed/mentioned real-world projects done
in Scheme.  I showed a movie of the real-time
writing-scheme-code-as-a-musical-performance work done by the Impromtu
team in Australia http://impromptu.moso.com.au/gallery.html.  I
discussed FP techniques practiced by Jane St. Capital, a Wall St
trading firm, http://portal.acm.org/citation.cfm?id=1394798.

In early November, I assigned preliminary work:  students had to
download and play with at least two different libraries from the
PLaneT repository. I demonstrated in class the HTTP Get library. We
also talked in class about project ideas, including the robotics,
gaming, and networking concepts that ultimately students implemented
(most networking stuff they did went far beyond any class

Just before Thanksgiving, their project proposal was due.  This was
supposed to be based on the exploratory work they had already
completed (and in many cases, it was).  In giving them the guidelines
for the proposal document, I also gave them the grading criteria for
the final project.  These were:

* an explicit connection to ideas that were introduced in the course
* an explicit connection to some outside piece of technology (e.g.,
images, sound, networking, database, etc)
* an interesting overall concept
* something that you personally are interested in and care about
* a writeup that explains what you accomplished
* a demo that lets people (or yourself) interact with your project

They had 2.5 weeks after the Thanksgiving holiday to work on their
projects for real.  In class, I was covering the metacircular
interpreter, and they had a problem set on this that was due 5 days
AFTER the project deadline had passed.  (This was a bit squeezed.)

I used the final class meeting date for a project open-house, which
was set up in our department's main lobby.  I provided drinks and
snacks for that, and we had a decent turnout, including several other

To me, the best projects were ones where students really did connect
Scheme and the course's ideas to something of personal interest.  As I
look back over the project list, I'd say that in more than half of the
projects, students really did something they were interested in, and
made explicit connections in their implementations to course material.
 (A number more did have the conceptual connections, but the thematic
matter was not really something the student was passionate about.)

As an example of a success story, there was a project where a student
imported baseball stats from a public web site into Scheme via XML
translation.  A number of students did stuff with XML, but this one
stood out because the student really cared about the baseball data.
He was really excited that he was able to reveal data that the web
site had collected, but did not make available in its standard web
presentation.  The project was not as advanced as some others, but
because of the student's true interest in the material, it was quite
well done.

(All the projects are written up at

Onto Shriram's questions:

> - This is an impressive list of projects, but how much evaluation was
> there of how well they did what they promised?

At the public demo day, I visited each project and had a 5-minute
conversation with each student, taking quick notes.  Then students
turned in their code, with additional documentation explaining it
(e.g., drawing out the ways their code exemplified ideas in the
class).  (BTW - I didn't make them post the code and notes on their
public project web pages.)

I graded their projects based on the criteria previously discussed
with them, with separate marks for: the quality of the proposal,
explicit connection to course concepts, use of external technology, an
innovation/creativity mark, the final writeup, and the quality of the
live demonstration.

I was lenient with the "did they do what they promised."  In fact, I
had told them that up front:  if you end up getting stuck or otherwise
needing to go in a different direction than you described in your
proposal, that was fine.  But I still used the same rubric for grading
(I just didn't penalize if it was different than the proposal).

> - How good is their code?  What's the measure of goodness?  Did they
> get administered code-walks?

This is a good/hard question.  As I mentioned earlier, one of my star
students commented that now he understood what people meant when they
were talking about "elegant code," and that he wanted to go back and
re-write code he had written in the past (code that was not written in
Scheme).  This was the person who built a hash table of lambda
functions to process a variety of possible reply packets from a
serially-connected hardware device.

So, to answer -- no there wasn't an administered code-walk.  That's a
great idea -- I wish I had time for that.  I did however read through
all of their code, and sync'ing that with their documentation notes,
was able to determine what kind of ideas they worked through in their
implementations.  This was the basis of the grading, particularly for
the "connection to course concepts" category.

One of the additional benefits of the project from my vantage point is
that it gave me a brand-new window into my students' abilities.  From
quiz scores and class participation, I could tell that about 1/3 of
the class was strong, and 1/3 was weak, but there was the middle band
that I was mentally lumping with the "weak" category -- they didn't
speak up in class, and their quiz scores were not great.

But from the projects, a bunch of this middle band really shined, and
I gained new appreciation for them.  As it turned out, they *were*
paying attention, and through the project, really engaged with the
class material.

So I'll definitely be running the projects again when I teach the
course in the spring.  I should be able to do a better job working
through the main curriculum so that the metacircular material (which
is clearly central) isn't so squeezed at the end.  Hopefully too I'll
be able to establish the value of the projects in my colleagues' eyes
so they have a chance of living beyond my tenure with the course.

There's one more Q&A below -- it's somewhat of a digression on
integrating Scheme and C++, so I'll end this note here and leave it as
a P.S.

Thanks again everyone for your attention and encouragement.


from Shriram:

> - Some of these remarks look a bit odd and unchallenged.  Eg, the
> Scheme-in-C-Game-Engine guy says,
>  In my opinion, using Scheme (or at least MzScheme) as a game
>  scripting language has some key disadvantages to more conventional
>  choices (such as LUA). The first of which is the
>  much-less-than-trivial embedding process. Of course, LUA was
>  specifically constructed with integration with languages such as C
>  in mind. Another disadvantage is the complex organization and
>  parenthetical syntax.
> The first few remarks are perfectly reasonable, as is the last one,
> but what does "complex organization" mean?  He should either write
> sufficiently clearly that a technically literate person can understand
> and evaluate the remark, or elide it.  (That is, the reader need not
> agree with all his statements, nor should he be uncritical; but he
> should be decipherable!)

This project was one of several in which students attempted to connect
Scheme with another language in a unified application.  This student
was the only one who was successful at this, and for two reasons: (1)
he chose to embed Scheme in a C++ app (and not the other way around),
and (2) he is a particularly strong coder.

I asked the student to clarify this, here's what he said:

> By "complex organization" I was referring to both the less-than-trivial
> embedding process, as well as having to build up "statements",
> "objects", and "methods" by first principles through Scheme in a way
> that is somewhat slow and deliberate (in order to achieve a customized
> effect) in comparison to other quick and dirty implementations of more
> out-of-the-box scripting solutions.

> I should point out that upon further messing around with the project in
> the past week or so, I have grown more and more fond of the level of
> customization that can be achieved with Scheme used as a scripting
> language.  The "complexities" I was referring to I now see as a valuable
> trade-off to achieve thorough customization.

There were several challenges to the embedding, but even after he was
technically successful, passing data back and forth between the two
language environments was hard.  He ended up using a simplified,
targeted representation of the game state that was constructed in C++
and handed off to Scheme.  But there was no straightforward way for
the two languages to share state.

Two other students tried incorporating C++ methods into Scheme, and
both failed to accomplish it on technical grounds.

The embedding-Scheme-in-C++ seemed better, but still not as satisfying
as one would like.

I'd be interested in hearing feedback on this particular thing, to see
whether to steer students away from this next time.

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