Type Checking

Semantic Analysis Validates Programs

After parsing, the compiler checks whether the program obeys language rules: types must match, variables must be declared, functions called correctly. Clang's Sema module and Java's javac attribution phase are large implementations of what you build in miniature.

What Type Checking Covers

Verify operators receive compatible operands (int + int, not int + struct). Ensure assignments match types. Confirm conditionals are boolean or truthy per language rules. Reject invalid implicit conversions before code generation.

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• Every expression node gets a resolved type annotation
• Errors attach to source locations from the AST
• Type rules are language-specific tables you encode
• Checking walks the tree bottom-up

Connecting to real compilers

Production compilers embed this step inside a longer pipeline. GCC flows through cpp, cc1, assembly, and ld; Clang uses the driver, Sema, LLVM IR passes, and a target backend. LLVM bitcode, JVM bytecode, and WASM are other familiar IRs at the same layer. The exercise isolates one pass so you can test it alone before chaining it to the next stage.

Why for this exercise

You will implement a type checker that walks the AST and validates operator and assignment types. This exercise asks you to annotate expressions with types and emit errors when language rules are violated.