How does yacc generate the syntactic parser from grammar rules?

I've understood how lexical analysis works,

but no idea how the syntactic analysis is done,

though in principle they two should similar(The only difference lies in the type of their input symbols, characters or tokens.) ,

but the generated parser code is greatly different.

Especially the yy_action,yy_lookahead,there's no such thing in开发者_JS百科 lexical analysis...

The grammars used to generate lexical analyzers generally are regular grammars, while the grammars used to generated syntatic analyzers generally are context-free grammars. Although they might look the same at the surface, they have very different characteristics and capabilities. Regular grammars can be recognized by deterministic finite automatons, which are relatively simple to construct and make fast. Context-free grammars are more challenging to build a recognizer for and usually a parser generator tool will construct a parser for only a subset of context-free grammars. For example, yacc constructs parsers for context-free grammars that are also LALR(1) grammars using push-down automata.

For more information on parsing, I would highly recommend Parsing Techniques, which walks through all the nuances of parsing in excruciating (but well described!) detail.