Use Yacc/Bison to Generate a Parser and Understand the Output

Parser Generators from Context-Free Grammars

Yacc and GNU Bison compile a context-free grammar plus semantic actions into an LALR or GLR parser table and C code. PostgreSQL's SQL parser, Bash, and countless domain languages are built with Bison. Understanding generated output demystifies shift/reduce conflicts.

Bison Workflow

Write a .y file: %token declarations, grammar rules with actions, %% separator, and user code. Bison emits yyparse(), token enums, and the ACTION/GOTO tables. Semantic actions build the AST as reductions fire.

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• %left and %right declare precedence and associativity
• $$ is the LHS value; $1, $2 are RHS slots
• Conflicts reported at generation time need grammar fixes
• Generated parser calls yylex() for tokens

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 use Yacc/Bison to generate a parser and study the emitted tables and C code. This exercise requires writing a grammar with semantic actions, resolving conflicts, and tracing how Bison's output drives parsing.