What is a DSL?

Submission deadline: Monday, Sept. 8 at 11:59pm

Critique deadline: Wednesday, Sept. 10 at noon

In this assignment, you'll read an introductory chapter about DSLs, which will give us some shared terminology for talking about DSLs and their implementations. Then you'll find a DSL "in the wild" and describe its design and implementation using terminology from the reading. Finally, you'll write a program in a cool DSL: ContextFree.

After this assignment, you should be able to:

• Recognize properties of a DSL, and evaluate those properties using common terms.
• Write in at least two DSLs (ContextFree and Markdown).
• Use GitHub as a submission system.

Teamwork

For the technical part of the assignment, you'll work by yourself (though you're free to talk about the assignment with anyone). For the critique part of the assignment, you'll pick a partner and review each other's work.

Read up on the assignment workflow

This article describes how we'll do our assignments on GitHub. Be sure to read it before you start working on your assignment.

Read Fowler's introduction to DSLs

Read Fowler, Chapter 2.¹ For the most part, this reading is self-contained. In a few places, Fowler references other parts of the book. Ignore these references; you can understand the reading without them. It may be helpful to know that, in Chapter 1, Fowler described a domain called Miss Grant's Controller. You can safely substitute the domain you choose for your DSL in place of Miss Grant's Controller.

¹ This copy of the reading is for class use only. You should not distribute it to anyone outside the class. You should destroy your digital copy when the class is over.

Find a DSL

Find a DSL---one that you think several other people in the class won’t know. When picking a DSL, it's good to find one for which you can find a few example programs, so you can get a good sense of it. Sometimes it's hard to be sure whether or not a language is actually a DSL. That's okay! If you find a language that you think might be a DSL, but you're not sure, then go with it---just assume that it is a DSL.

Describe your DSL

Open the file my-dsl.txt, read the questions there, and edit the file to include your answers to those questions. Back up your answers with any evidence that you can find about your DSL. Your answers must be formatted in markdown.

Note: there are many different kinds of markdown. If you already have a favorite kind of markdown, feel free to use it. If you don't have a favorite, you can use the same markdown that we use on the wiki.

Learn, use, and critique ContextFree

1. Download ContextFree, a domain-specific language for making art. You should download version 2.2, which is not the current version of the language. (download: Windows, Mac, Linux). Note: the Mac version is also installed on the CS lab Macs. The version 2.2 documentation is [here](http://contextfreeart.org/mediawiki/index.php/ Version_2_Syntax).

2. Write an interesting ContextFree program. Save your program in a file called firstname_lastname.cfdg (where you fill in your first and last names, of course).

3. Export a nice image from your program. (Choose the Render menu, then Save Image...) Use a .png extension, so your filename should be firstname_lastname_variant.png (where variant is the three-letter variant the uniquely identifies this version of your program).

4. Answer the questions in context-free.md.

Peer-review your partner's work

Once your partner has submitted, you can comment on their work. You should provide feedback on all aspects of your partner's work, including the information in my-dsl.md, context-free.md, their code, and their image. Here are some questions you might consider / answer when providing feedback:

• Would you answer a question from the assignment differently than your partner did? For example, do you agree with how your partner described the DSL-ness of their language?
• Did your partner describe anything that you also experienced? For example, did you try to do something in ContextFree that was difficult?
• If your partner has raised a question in my-dsl.md or context-free.md, try to answer it!
• Did you learn any cool language features (from ContextFree or Markdown) that might add to your partner's work?

Tasks

• Identify a partner for the critique part of the assignment
• Read the Assignment HOWTO
• Read Fowler's introduction to DSLs
• Find a DSL
• Describe your DSL's implementation and semantics in my-dsl.md
• Write a ContextFree program in firstname_lastname.cfdg
• Make and save a pretty picture in firstname_lastname_variant.png`
• Answer the questions in context-free.md
• Submit your work
• Comment on your partner's work