TITLE: A Positive Story at the End of a Long Year
AUTHOR: Eugene Wallingford
DATE: April 23, 2021  3:59 PM
DESC: 
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BODY:
 This is short story about a student finding something helpful
 in class and making my day, preceded by a long-ish back story.

 In my programming languages course yesterday, I did a session
 on optimization.  It's a topic of some importance, and students
 are usually interested in what it means for an interpreter or
 compiler to "optimize" code.  I like to show students a
 concrete example that demonstrates the value of an optimization.
 Given where we are in the course and the curriculum, though, it
 would be difficult to do that with a full-featured language
 such as Python or Java, or even Racket.  On the other end of
 the spectrum, the little languages they have been implementing
 and using all semester are too simple to benefit from meaningful
 optimization.

 I found a sweet spot in between these extremes with
<a href="https://en.wikipedia.org/wiki/Brainfuck">
   BF</a>.
 (Language alert!)  I suppose it is more accurate to say that
 Eli Bendersky found the sweet spot, and I found Bendersky's
 work.  Back in 2017, he wrote a series of blog posts on how to
 write just-in-time compilers, using BF as his playground.
<a href="http://eli.thegreenplace.net/2017/adventures-in-jit-compilation-part-1-an-interpreter.html">
   The first article in that series</a>
 inspired me to implement something similar in Python and to
 adapt it for use with my students.

 BF is well-suited for my purposes.  It is very simple language,
 consisting of only eight low-level operators.  It is possible
 to write a small interpreter for BF that students with only a
 background in data structures can understand.  Even so, the
 language is Turing complete, which means that we can write
 interesting and arbitrarily complex programs.

 The low-level simplicity of BF combines with its Turing
 completeness to create programs that are horribly inefficient
 if they are interpreted in a naive manner.  There are many
 simple ways to optimize BF programs, including creating a
 jump table to speed up loops and parsing runs of identical
 opcodes (moves, increments, and decrements) as more efficient
 higher-level operators.  Even better, the code to implement
 these optimizations is also understandable to a student with
 only data structures and a little background in programming
 languages.

 My session is built around a pair of interpreters, one written
 in a naive fashion and the other implementing an optimization.
 This semester, we preprocessed BF programs to compute a table
 that makes jumping to the beginning or end of a loop an O(1)
 operation just like BF's other six primitives.  The speed-up
 on big BF programs, such as factoring large numbers or
 computing a Mandelbrot set, is impressive.

 Now to the story.

 At the end of class, I talk a bit about
<a href="https://en.wikipedia.org/wiki/Esoteric_programming_language">
   esoteric languages</a>
 more broadly as a way for programmers to test the boundaries
 of programming language design, or simply to have fun.  I get
 to tell students a story about a four-hour flight back from
 OOPSLA one year during which I decided to roll a quick
 interpreter for
<a href="https://esolangs.org/wiki/Ook!">
   Ook</a>
 in Scheme.  (What can I say; programming is fun.)

 To illustrate some of the fun and show that programmers can be
 artists, too, I demo programs in the language
<a href="https://en.wikipedia.org/wiki/Esoteric_programming_language#Piet">
   Piet</a>,
 which is named for the Dutch abstract painter
<a href="https://en.wikipedia.org/wiki/Piet_Mondrian">
   Piet Mondrian</a>.
 He created paintings that look like this:

 <center>
 <img src="http://www.cs.uni.edu/~wallingf/blog-images/code/piet-in-piet.gif"
      alt="a Piet program that prints 'Piet'"
      align="center"
      width="160">
 </center>

 That is not a Mondrian, but it is a legal program in the Piet
 language.  It prints 'Piet'.  Here is another legal Piet
 program:

 <center>
 <img src="http://www.cs.uni.edu/~wallingf/blog-images/code/piet-hello-world.png"
      alt="a Piet program that prints 'Hello, World'"
      align="center"
      width="160">
 </center>

 It prints "Hello, World".  Here's another:

 <center>
 <img src="http://www.cs.uni.edu/~wallingf/blog-images/code/piet-prime-test.gif"
      alt="a Piet program that determines if a number is prime"
      align="center"
      width="160">
 </center>

 That program reads an integer from standard input, determines
 whether it is prime or not, and prints 'Y' or 'N'.  Finally,
 how about this:

 <center>
 <img src="http://www.cs.uni.edu/~wallingf/blog-images/code/piet-tetris.png"
      alt="a Piet program that prints 'tetris'"
      align="center"
      width="160">
 </center>

 If you are a certain age, you may notice something special about
 this image:  It is made up exclusively of Tetris pieces.  The
 program prints... "Tetris".  Programming truly is an art!

 One of my students was inspired.  While reviewing the session
 notes, he searched for more information about Piet online and
 found
<a href="https://gabriellesc.github.io/piet/">
   this interactive editor</a>.
 He then used it to create a Piet program in honor of a friend of
 his who passed away earlier this semester.  It prints the Xbox
 gamertag of his late friend.  In his email to me, he said that
 writing this program was therapeutic.

 I'm not sure one of my class sessions has ever had a more
 important outcome.  I'm also not sure that I have ever been
 happier to receive email from a student.

 This has been a tough year for most everyone, and especially
 for students who are struggling with isolation and
 countermeasures against a nasty virus.  I'm so glad that
 programming gave one student a little solace, at least for
 an evening.  I'm also glad he shared his story with me.
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