Held Monday, August 28, 2000
Today we continue our exploration of computer science by writing our
first algorithm and considering issues of formal languages.
- If you haven't done so already, please fill out the
- My preliminary
responses to your questions are now available.
responses to the CS152 survey are also available.
You can even
learn about some of my undergraduate grades.
- Thanks to those of you who reminded me to consider multicultural
issues in my teaching style. I hope that most of you can deal
with my somewhat informal style.
- For those of you who are concerned: most of you are at the beginning
level, having used computers primarily for word processing, games,
and sometimes surfing the 'net.
- I was impressed that at least one of you read
my CV and
at least one of you read my list of
listened to recently.
- Every Monday at noon, the department hosts a brown-bag film festival
at noon. See interesting talks by great computer scientists. (Okay,
sometimes you see mediocre talks by great computer scientists, but then
we all make sarcastic comments.) I'm pretty sure that you can pick
up a bag lunch if you're on meal plan.
- If you've talked to students in the other section of 151, you may have
noted that the two sections are following a different schedule (with
some difference in topics). Each faculty member teaches 151 differently.
We're starting Scheme a little bit after the other section, but we'll
catch up after a few weeks.
- My wife managed to break a toe yesterday, so I won't be in my office
during office hours today.
- Why are you here?
- The need for formal languages
- HTML: A formal language for representing hypertexts
- Paradigms for programming and problem solving
- I wrote the question on the board, but never got to it in class.
- I also wrote the question on the survey, but I'd like to hear some
- So, we'll go back to the hat trick for volunteers.
- Some people wonder why we need computer languages like Scheme, Pascal,
C, Java, and the ilk.
- In part, it's probably because the computer elite want to maintain
their sense of superiority over the masses.
- In greater part, it's because English and other ``natural'' languages
can be ambiguous. At the very least, they have many similar structures
that are interpreted very differently. Consider the classic pair of
- Time flies like an arrow.
- Fruit flies like a banana.
- As I've said (and will say again), computers are sentient and malicious.
it often seems that they'll do their best to misinterpret whatever it
is you write.
- As an exercise, we're going to write a set of instructions that would
help a foolish person (SamR) make a peanut butter and jelly sandwich.
- One person will be the recorder.
- I'll use the hat trick to get people to write it.
- I'll then follow your instructions to the best of my ability.
- You will then have a chance to refine your instructions.
- I apologize in advance for any food wasted.
- Now that we've established the need for formal languages, we need to
think a little bit about the design of such languages.
- It turns out that there are different ways of thinking about problem
solving, and these different ways of thinking lead to different
types of languages. (We often call these problem-solving paradigms.)
- Computer Scientists have developed a number of strategies for looking
at algorithm and data design, including
- procedural / imperative
- While individual definitions of each category may differ, most
definitions have some similarities.
- In the imperative paradigm, algorithms are sets of instructions
not unlike standard recipes. Do this. Do that. Do whatever N times.
- Common imperative languages: Ada, Basic, C, Fortran, Pascal
- In the object-oriented paradigm, algorithms are sets of objects
that interact. Most typically, objects are reactive: They exectute
algorithms in response to events that happen. For example, most of
you have an algorithm that says "When the instructor asks for volunteers,
scrunch down in my seat."
- Common object-oriented languages: C++, Java, Smalltalk
- In the functional paradigm, programs are collections of
function definitions and function applications. At times,
functional programming feels mathematical, but it can also
be used in many other domains. You may remember dealing with
the compose function in mathematics. Surprisingly enough, functional
languages are the only ones that include something like compose.
- Common functional languages: Haskell, LISP, ML, Scheme
- In the declarative paradigm, programs are collections of
facts. Behind the scenes, there is something that knows how to
deal with the facts. For example, we can give an experienced
baker a list of ingredients for cookies and not worry about formal
- Common declarative languages: Prolog, SQL
- As an example, we'll consider the problem of updating grades using
each of the paradigms.
- At Grinnell, we deem it important that students study a variety
of paradigms early in their careers, whether or not they are
computer science majors.
- As I said before, thinking differently is part of a liberal arts
- In CS151, you will study functional and imperative programming.
- If you go on to CS152, you will study object-oriented and imperative
Thursday, 24 August 2000
- Created as a blank outline.
Sunday, 27 August 2000
- Filled in the details. The (now-deleted) section on HTML was primarily taken from
outline 3 of my fall 1999 Tutorial.
Monday, 28 August 2000
- Slight updates, particularly to introductory notes.
Tuesday, 29 August 2000
- Moved section on HTML to the next outline.
Back to Introduction to the Course.
On to HTML: A Formal Markup Language.