Project, Phase 3: Type Checker

Assigned: Friday, 2 April 2004
Due: Friday, 16 April 2004

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

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

Preparation:

• You need only deal with a subset of Pascal. Read the notes on simplifying Pascal.
• Review the type checking lab to see the form of a simple type checker.
• Look at the rebelsky.compiler.types library for the type objects you can put in your symbol table.
• Look at SymbolTable.java, a simple symbol table implementation. You will most likely need only setType, getType, beginScope, and endScope.

Core Assignment

Write a type checker that traverses parse trees for Pascal problems and

• (1) gathers type information on constants, variables, the parameters to procedures, and functions, and the return type from functions;
• (2) checks expressions, assignment statements, and procedure calls for type correctness;
• (3) prints error messages when it encounters type errors (you can stop at the first type error);
• (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; and
• (6) returns a value that indicates whether or not the parse tree is type correct.