Thread: [Flex/Bison] Handling newlines

I'm not sure if a C programming forum is the right place to ask something regarding Flex and Bison, but people around here have been very helpful in the past so I decided to give it a try.

So, we're required to create a lexical & semantics parser as part of the Compilers course, using Flex and Bison. My issue is that I don't have a proper way to handle newlines. We're required to ignore all whitespace and newlines except if specifically asked, so I did the simple thing and had my Flex file return nothing in case of whitespace. But there is a certain rule in the language we're asked to parse that requires a newline character at the end of the line.

Rule goes something like this:

Code:

program: PROGRAM variable_name newline

That's the only rule that specifically requires a newline. Everywhere else we're asked to ignore it. So what's a proper way of requiring the newline there, but having it ignored everywhere else so that I don't have to add optional "newline" rules in every rule that I have in my syntax?

Sounds like you want one function to handle all the newlines. Then,

Code:

if (first word in the line is "program: ")
  ; //do nothing
else
  delete the newline

If you have logic to handle newlines spread all over, when specifically asked not to ignore them, you're going to have a mess on your hands - no doubt.

Just a general note - I don't know Flex/Bison.

Yeah, that sounds logical. newline character detected in flex should call a function in bison which should be able to tell if the newline character was read after the program's name, and if so return it (accept it), or else ignore it.

If only I knew how to do something like that in Flex/Bison.

:P

Many thanks. I realized what I had to do reading your suggestion before looking at the code snippet, but it was exactly that.

Really, many thanks.