Recursive Descent Parser

Recursive Descent Is the Default Hand Parser

Most production parsers start as recursive descent: one function per grammar rule, mutual recursion for expressions and statements. Python's parser, many DSL compilers, and Clang's early parsing paths use this style because it maps directly onto the grammar and produces great errors.

One Function Per Rule

Write parse_expression(), parse_statement(), parse_function() that consume tokens and return AST nodes. Each function checks the current token, dispatches on it, and recursively calls sub-parsers. Left recursion in the grammar must be rewritten or handled with precedence climbing.

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• peek() inspects without consuming; advance() moves forward
• Match expected tokens or report syntax error
• Build AST nodes bottom-up as you return from recursion
• Expression parsing often delegates to Pratt or precedence layers

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 recursive descent parser that consumes your lexer's token stream and builds an AST. This exercise requires parsing expressions with correct operator precedence and handling statements, function declarations, and blocks.