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TheProgramByDesign (formerlyTeachScheme!) project is an outreach effort of thePLT research group. The goal is to train college faculty, high schoolteachers, and possibly even middle school teachers, inprogramming andcomputing.
Matthias Felleisen andPLT began the effort in January 1995, one day after theSymposium on Principles of Programming Languages (POPL), in response to Felleisen's observations of hisRice University freshmen students and the algebracurriculum of local public schools. His objective was to usefunctional programming to makemathematics come alive and help inject design knowledge into the introductorycomputer science curriculum.
The effort began using aprogramming language named PLT Scheme which was a version of the languageScheme, which is adialect ofLisp.
The group raised funds from several privatefoundations, theUnited States Department of Education, and theNational Science Foundation to create:
Over ten years, it ran several dozen one-weektraining workshops for some 550 teachers. In 2005, the TeachScheme! project ran an Anniversary workshop where two dozen teachers presented their work with students.
In 2010, PLT renamed its major programming language fromPLT Scheme toRacket, andDrScheme toDrRacket. A little later it renamedTeachScheme! toProgramByDesign.
The starting point of ProgramByDesign is the observation that students act as computers inprimary school courses on arithmetic, and inmiddle school andsecondary school courses onpre-algebra andalgebra. Teachers program them with rules and run specific problems via exercises. The key is that students execute purely functional programs.
If students can be turned into teachers that create functional programs and run them on computers, this content can be reinforced and show students how writing down mathematics, and functional programs, creates lively animated scenes and even computer games.
Here is an example:
(require2htdp/universe)(require2htdp/image);; create an image from the current time(define(create-imaget)(place-imageAPPLE50(*1/10tt)SPACE));; names for basic images(defineAPPLE(circle3"solid""red"))(defineSPACE(empty-scene100100))(animatecreate-image)
This short program simulates an apple falling from the top to the bottom of a small white canvas. It consists of three parts:
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 andn columns where each column containst 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 animate line applies the given function, create-image, at the rate of 28 ticks per second to 0, 1, 2, 3, and so on. The resulting images are displayed on the computer monitor at the same pace. 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 DrRacket (which is like the one for numbers), and minimal pre-algebra. The ProgramByDesign project claims, however, that children would have more fun with suchlive functions than with algebraic expressions that count the number of garden tiles [see Prentice Hall books for grades 8-9].
The ProgramByDesign project proposes that both traditional mathematics and science courses could benefit from integrating this form of programming. In contrast to the traditionalBASIC orVisual Basic blocks in such books, a Racket 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. DrRacket's algebraic stepper can illustrate how Racket evaluates the program as if it were a sixth or seventh grade student, step by step, using plain algebra.
For the introductory curriculum on programming, the ProgramByDesign 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 whether they become programmers or doctors or journalists or photographers. Thus, an introductory course in programming would not be perceived as a place where students learn about the syntax of the currently fashionable (and soon-to-be-obsolete) programming languages, but a place where they can learn something widely applicable.
The key design element of the ProgramByDesign curriculum is thedesign 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:
As intest-driven development, test cases are writtenbefore coding, as part of requirements analysis, rather than afterward as part of testing.
Almost any human endeavour can benefit from clearly understanding the problem, defining criteria for success, analyzing the available resources and givens, developing a proposed solution, and checking it against the criteria, in that order.
For example, a journalist benefits from a similar process: figuring out the major concepts in a story; creating a headline; lining up examples and specific data; organizing the article about the story of the givens and how the story unfolded; writing; and fact checking.
The data dimension can be summarized by the maximthe shape of the data determines the shape of the code and tests. For example, if the input or output data type has three variants, a test suite should have at least one test case from each variant, and program code will probably contain a three-way conditional (whether explicit or hidden in a polymorphic dispatch). If the input or output data type has three fields, a test suite will have to specify values for those three fields, and program code will have to refer to those three fields. If the input or output data type has a simplebase case and one or more self-referential variants, the test suite should include a base case and one or more non-base cases, and the program code will probably have a base case and one or more self-referential cases, isomorphic to the data type. The technique ofrecursion, rather than being mysterious and scary, is simply applying already-learned methods to a self-referential data type.
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 (HTDP) is the text book authored by the core of the ProgramByDesign group.[1] A third edition is being prepared.[2]
The name TeachScheme! appears to imply that this design recipe requires Scheme (nowRacket) and is teachable only with Scheme. Neither conclusion is true. Members of PLT and their trainees have successfully applied the design recipe inassembly language,C,Java,ML,Python, and other programming languages, and with geometry, biology, and poetry courses. The fundamental idea of ProgramByDesign is to stress programming as a design activity. This misconception is one of the reasons for the renaming actions taken in 2010.
To get started, the ProgramByDesign project has produced three essential elements:
Their choice of Racket reflects their belief that Racket is a good language for a small team with little funding (relative to Java) to validate their conjectures. The PLT group has always tried to ensure that the ideas remain portable to other contexts.
Over the past few years, the team has also created a second part or phase of the curriculum. It demonstrates how the same design recipe ideas apply to a complexobject-oriented programming language, such asJava. The recipes are applied initially in a functional paradigm, then introducing object-oriented concepts such as polymorphism and inheritance, and then introducing the imperative methods that are idiomatic in mainstream Java.
A part of the team has a grant from the National Science Foundation to conduct field tests in colleges and high schools.Professional development workshops took place in the summer of 2007, 2008, 2009, and 2010. This part of the project is dubbed ReachJava; the accompanying book is tentatively titled "How to Design Classes."
In 2006 PLT, at Northeastern University andCitizen Schools from Boston, made joint efforts to reach out to inner city students with after-school programs. Citizen Schools is a nationwide organization that matches volunteers with after-school program sites and gets them started with scripted curricula. The goal of the effort is to translate the material into a sixth-grade curriculum. The first few tests were a great success in Boston.[3][4] The effect on the mathematics courses of this program has encouragedMicrosoft andGoogle to fund a national scale-up effort, developing materials for training teachers and creating sites in Texas, California, and other volunteer cities.
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