Implement Function Signature Checking (Argument Count and Types)

Call Sites Must Match Declarations

Before ANSI C prototypes, calling foo(1, 2, 3) when foo expected two ints was undefined behavior. Clang's Sema checks arity and parameter types on every call. The Linux kernel builds with -Werror=implicit-function-declaration because signature mismatches cause real production bugs.

Three Checks at Every Call

Look up the function in the symbol table. Verify argument count equals parameter count. For each position, verify the argument type is compatible with the parameter type, applying permitted coercions (e.g., int to float).

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• Store return type and parameter type array per function
• Report distinct errors for wrong count vs wrong type
• Handle unknown function separately from wrong signature
• Coercion rules are language-specific

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 function signature checking that validates argument count and types at call sites. This exercise requires storing signatures in your symbol table and comparing each call against the declared parameter list.