Once the Lexer has converted a C programs characters to a series of tokens, the compiler must check if the order of these tokens lead to valid statements. For this, the Parser is used.
The Parser is passed the tokens from the Lexer then uses a set rules called grammars to check whether valid statements are being passed. For example say the Lexer converts the C code “return a;” to “RETURN ID SEMICOLON”. The Parser would have a grammar to recognize this pattern tokens:
return_st: RETURN ID SEMICOLON {;}Note, Bison will be used to implement the Parser for the XM3 compiler. Bison is an open source tool used with Flex.