Hints on Writing Syntax (like in the CS320 project)

1. Read, copy, and think about the sample syntax descriptions that are on the WWW.

2. Go back to chapter 3. It is theoretical -- but there is nothing quite so reusable as a good theory.

• 2a. Look at how precedence and associativity are expressed.

• 2b. Look at the way recursion and iteration({}, #) is used.

• 3a. Start with examples of what you want.

• 3b. Finish by adding comments explaining why each piece of syntax is useful.

• 4a. Don't forget you can use these words in a name: optional, body, head, foot, end, part, ...

• 4b. Spell check the syntax!

• 4c. Avoid words like: compile, execute, etc that describe semantics.

6. Write your syntax first and then check it for ambiguity afterwards. See Chapter 3. Ambiguous syntax reduces people's belief in your abilities. It makes implementation impossible.

7. Present your work to others. Ask for improvements. Listen to their criticism. Improve your documentation.

8. Write syntax as if you where explaining the language to a mathematical but naive child.

9. Practice Makes Perfect Use the XBNF notation to define

• Input and output data for programs you are about to design.

   		input::=#char.

   		output::=#char.

• Communication protocols (output from one program to another program on the network)
• Program structures

   		program::= open_files #copy_one_char close_files.

• Valid sequences of calls to methods for an object.

   		counter::=construct #( #(count|get) set  ) destruct.

• Expressions in any commutative semi-ring!

To review syntax description: write your own XBNF for some construct you know well and compare it with the versions in the languages reference manual and on the WWW.