如何在 jflex 上创建一个 lambda 符号？

Question

I'm doing a syntactic Analixer with jflex + javacup. At the .cup gramatic I have this part:

   SUBPPARAMLIST ::= lambda | "(" EXPLIST ")"

Where lambda mean nothing (SUBPPARAMLIST can be empty)

Well, I managed to create all my tokens correctly in my .flex, but I dont know how to create the lambda symbol. I hope you guys can help me, let me know if you dont understand my problem

WhatDoIWriteHere{return symbol(sym.lambda);}

Answer 1

The empty production (what you call "lambda") doesn't need a symbol, because it is empty. You express this by a production rule:

SUBPPARAMLIST ::= lambda | "(" EXPLIST ")" ;
lambda ::=  ;

Quote: Each production in the grammar has a left hand side non-terminal followed by the symbol "::=", which is then followed by a series of zero or more actions, terminal, or non-terminal symbols, followed by an optional contextual precedence assignment, and terminated with a semicolon (;). Note the "...zero or more..."

Possibly the grammar parser is also capable of handling this:

SUBPPARAMLIST ::= "(" EXPLIST ")" | ;