[antlr-interest] How do I accept input ending with a newline *or* EOF?

[Micha]

Am 04.02.2011 04:21, schrieb chris king:
> Suppose I want to create a grammar to recognize integers with one integer
> per line. Additionally suppose I want a preprocessor such that I can wrap
> groups of integers in #if [expr] ... #endif where if expr has basic
> arithmetic operations. If expr evaluates to greater than 0 the enclosed
> lines are lexed else they are not. What would that grammar (or even just
> lexer) look like?
> 
> So for example, it should recognize this input and return an integer token
> 10 but not a token for 20. It should also ignore the comment.
> 
> 
> 10
> #if (2-1)*3-10
> 20 and just ignore this comment
> #endif
> 
> I cannot come up with a lexer that can lex the whole file without knowing if
> it's in an active #if\#endif block so I'm stuck before I can even begin my
> grammar.


I think it would be better to open a new thread for a new question :-)

The lexer itself isn't that suited to capture blockstructures, but if
you really want to do it, you can maintain yourself a stack of states,
onto which you push something like 'IN_BLOCK' after seeing the #if and
remove it after seeing the #endif  (if you want to nest the blocks)
You lex the tokens as normal, but when inside a block you return just a
NL or similar. You could use this to prescan the input ....
Maybe some book about compiler construction or DSL could help also (the
antlr dsl book is really helpful)

cheers,
 Michael