So I have a grammar that includes the empty string. The grammar is something like this:
S->ε
S->expression ;; S
I'm getting the error "No more states to discard" when I run my parser so I believe I'm not representing the empty string correctly. So how would I go about representing it, specifically in the lexer .mll file?
I know I need to make a rule for it so I think I have that down. This is what I think it should look like for the parser .mly file, excluding the stuff for expression.
s:
| EMPTY_STRING { [] }
| expression SEMICOLON s { $1::$3 }
You're thinking of epsilon as a token, but it's not a token. It's a 0-length sequence of tokens. Since there are no tokens there, it's not something your scanner needs to know about. Just the parser needs to know about it.
Here's a grammar something like what I think you want:
Note that
epsilon
is a non-terminal (not a token). Its definition is an empty sequence of symbols.