Implement Error Recovery: Continue Parsing After Syntax Error

Parsers Should Survive Syntax Errors

A parser that stops at the first syntax error frustrates users fixing large files. GCC and Clang use panic-mode recovery and synchronization tokens (semicolons, braces) to skip to a safe point and continue. Rust's parser reports multiple errors in one run using similar techniques.

Synchronization Points

On unexpected token, report the error, then skip tokens until a synchronizing token appears: ;, }, or a statement keyword. Resume parsing at the next statement boundary. Insert an error node in the AST if you need to preserve structure.

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• Never consume tokens in an infinite skip loop without advancing
• Record error location and expected vs actual token
• Panic mode is simple; error productions in LR parsers are more precise
• Recovery enables multiple diagnostics per compilation

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 add error recovery to your parser so syntax errors do not abort the entire parse. This exercise asks you to synchronize at statement boundaries and continue building a partial AST after reporting each error.