The techniques described in Challenge Exercise 1 also work for the parsing phase of the compilation process. That is, instead of writing a parsing program, we can provide data to an already written program that will do the job for us. A special program called a parser generator, also called a compiler-compiler, can act as a universal parser for any language that can be described using BNF notation. To use a parser generator, you simply input the productions of the grammar of your language and the sequence of tokens to be parsed. The output of the parser generator is a parse tree if the sequence of tokens is legal according to your productions, or an error message if it is not.

The most widely used parser generator is a program called yacc, an acronym for “Yet Another CompilerCompiler.” Yacc, like lex, has been used to build a great number of compilers. Read about parser generators and yacc, and write a report describing how yacc works and how you formally represent BNF productions. If you have yacc available at your installation, enter the BNF rules for and let yacc parse the statement

x = y + z;