Project, Phase 3: Type Checker

Assigned: Friday, November 8, 2002
Due: Wednesday, November 20, 2002

This assignment is optional!

Summary: In this stage of the project, you will design and build a portion of the the type checker for your Pascal compiler.

Group Work: You should work with the same group that you worked with for the parser.

Core Assignment

Write a type checker that traverses parse trees for Pascal problems and (1) gathers type information on constants, variables, and the return type from functions; (2) checks expressions and assignment statements for type correctness; (3) prints error messages when it encounters type errors; (4) inserts appropriate coercion nodes to convert between types (e.g., from integers to reals); (5) adds a type attribute to each appropriate node in an expression; returns a value that indicates whether or not the parse tree is type correct.

Your type checker need only deal with integers, reals, and Booleans. That is, you don't need to deal with user-defined types, with records, or with arrays. Your type checker does not need to check the parameters function or procedure calls. Your type checker does need to use the return value from functions in checking expressions.

You can use my implementation of symbol tables, which should be ready by the end of today. (Expect a link and an email message.)

Extra Credit

For extra credit, do more than the minimum. For example, you could

• Support user-defined enumerated types.
• Support arrays (index type and content type).
• Support records.
• Type check function and procedure parameters.