ProgramByDesign

The TeachScheme! project is an outreach effort of the PLT research group. The goal is to train college faculty, high school teachers and possibly even middle school teachers in programming and computing.

History

Matthias Felleisen and PLT started the effort in 1995 (January, one day after the POPL symposium) in response to observations of his Rice freshmen students and the algebra curriculum of local public schools. His objective was to use functional programming to bring mathematics alive and to help inject design knowledge into the the introductory computer science curriculum.

The group raised several million dollars in funding from foundations, the US Department of Education, and the National Science Foundation to create

• software appropriate for novices in functional programming
• courseware (curricula, lecture notes, exercises, mini-projects)
• teacher training camps.

Over ten years, it ran several dozen one-week workshops for some 550 teachers. In 2005, the TeachScheme! project ran an Anniversary workshop where two dozen teachers presented their work with students.

Functional Programming, Computing and Algebra

The starting point of TeachScheme! is the observation that students are computers in grade school courses on arithmetic and middle/high school courses on pre/algebra. Teachers program them with rules and run specific problems via exercises. The key is that students execute purely functional programs.

If we can turn students into teachers that create functional programs and run them on computers, we can reinforce this content and show students how writing down mathematics and how writing down functional programs creates lively animated scenes and even computer games.

Here is an example:

;; create an image from the current time 
(define (create-image t) (place-image APPLE 50 (* 10 t) SPACE))

;; names for basic images 
(define APPLE (circle 3 'solid 'red))
(define SPACE (empty-scene 100 100))

;; --- run program run: 
(run-simulation 100 100 1/22 create-image)

This four-line program simulates an apple falling from the top to the bottom of a small white canvas. It consists of three parts:

• a function definition for create-image, which is a one-line function in

mathematics, assuming an algebra of images with place-image, circle, and empty-scene have been introduced;

• two abbreviations, where names are equated with some value, just as in "let x be

5" in an algebra text; and

• one line for running the program.

A teacher can explain create-image as easily as any ordinary function in an algebra course. For example, one can first draw a table with two rows and n columns where each column contains t at the top and an appropriate image at the bottom. That is, if the numbers increase from left to right, then on each image the red dot is a little bit lower.

Finally the run-simulation line displays the images on a 100 x 100 canvas at the rate of 22 images per second. That's how movies are made.

The background needed for such an example is little more than knowledge about making movies, about the algebra of pictures in DrScheme (which is like the one for numbers), and minimal pre-algebra. The TeachScheme! project claims, however, that children would have more fun with such "live" functions than with algebraic expressions that count the number of garden tiles [see Prentice Hall books for grades 8-9].

The TeachScheme! project proposes that both traditional mathematics as well as science courses could benefit from an integration of this form of programming. In contrast to the traditional Basic or Visual Basic blocks in such books, a Scheme program consists of as many lines as the mathematics. Moving between the mathematics and the program is thus straightforward. Better still, the meaning of the two are the same. DrScheme's algebraic stepper can illustrate how Scheme evaluates the program as if it were a sixth or seventh grade student, step by step, using plain algebra.

Functional Programming, Computing and Design in Programming 101

For the introductory curriculum on programming, the TeachScheme! project emphasizes that courses should focus on the role of systematic design. Even if students never program again, they should see how helpful a systematic approach to problem solving is. This should help them if they become programmers or doctors or journalists or photographers. Thus, an introductory course in programming would not be perceived a place where students learn about the syntax of the currently fashionable programming languages, never to be remembered, but a place where they can learn something that is applicable elsewhere.

The key design element of the TeachScheme! curriculum is the design recipe. It has two dimensions: the process dimension and the data dimension.

Along the process dimension students learn that there are six steps to designing a (simple) program, before they can run it and others can use it:

• problem analysis with the goal of describing the classes of data that go into the program and come out;
• the reformulation of the problem statement as a concise purpose statement;
• the creation of examples that illustrate the purpose statement;
• the organization of givens, also called a template or inventory;
• coding;
• and the creation of a test suite from examples to ensure the program works

properly on small inputs. A close look at these steps shows how even a journalist, for example, benefits from a similar process: figuring out the major concepts in a story; coining a headline; lining up examples and specific data; organize the article about the story around the givens and how the story unraveled; writing; and fact checking.

Organizing the givens is the task of translating the descriptions of data into a program skeleton. Each form of description determines a specific form of program organization. The transformation is nearly mechanical and helps the students focus on the creative part of the task.

How to Design Programs is the text book authored by the core of the TeachScheme! group.

TeachScheme! and Scheme

While the name TeachScheme! appears to imply that this design recipe requires Scheme and is only useful with the Scheme, it is actually a pun for computer scientists who know post-fix notation: teach Scheme, not. Neither the process nor the data axis of the design recipe require the use of Scheme. The TeachScheme! members and their students have successfully applied the design recipe in Assembly, C, Java, ML, Python, and other programming languages, not to speak of poetry, geometry, and biology courses.

To get started the TeachScheme! project has produced three essential elements:

• a series of teaching languages, which are dialects of Scheme, matched to the

design recipe but with much better error reporting than a plain Scheme implementation;

• a pedagogic programming environment that helps students grow from Beginning Scheme

to Intermediate, Advanced and plain Scheme;

• a curriculum.

Their choice of Scheme reflects their belief that Scheme is a good language for a small team with little funding (in comparison to Java) to validate their conjectures. The PLT group has always ensured, however, that the ideas remain portable to other contexts.

From TeachScheme! to ReachJava

Over the past few years, the team has also created a second part of the curriculum. It demonstrates how the same design recipe ideas apply to a complex object-oriented programming programming language, such as Java.

A part of the team has raised money for conducting field tests with college faculty and high school teachers. The first trial workshops took place in the summer of 2007. This part of the project is dubbed ReachJava; the accompanying book is tentatively titled "How to Design Classes."

External links

• TeachScheme! website: http://www.teach-scheme.org/
• PLT Scheme: http://www.plt-scheme.org/
• How to Design Programs: http://www.htdp.org/