Hehe, okay, here I go. :)
I'm trying to replace an existing flex/bison parser with an re2c/lemon
parser, but I'm running into a methodological problem. I have a
hypothetical grammar like this:
file ::= FOO str .
file ::= BAR str .
Where my keywords are FOO and BAR, and str is any ol' generic string.
I'm giving it the input "FOO BAR" in the hopes that it will match the first
rule and give str the value "BAR". To keep Lemon from choking on a syntax
error when it sees BAR, I want to tell the lexer (re2c) to force the next
token after "FOO" to be a string. Thus I broke the rule up like so:
file ::= fooDefinition .
fooDefinition ::= fooStart fooEnd .
fooStart ::= FOO . { lexer->forceNextThingToBeAString(); }
fooEnd ::= str .
However, the call to forceNextThingToBeAString() happens after re2c reads
"BAR", and by that time it's already identified it as the keyword BAR
instead of as a string that happens to be set to "BAR". It seems like Lemon
always reads a lookahead token, even though it doesn't need to.
I considered using the lexer-only hack of having the lexer force a string
after "FOO", but that only works if every FOO in the grammar is followed by
str. In my real-world problem, that's not the case. The CFG of the lexer
is not adequate to know when to force strings; it requires control from the
parser.
Would you have any comments/ideas?
Thanks!
-Chris
On Tue, Apr 6, 2010 at 1:12 PM, Wilson, Ronald <rwils...@harris.com> wrote:
> > I'm using the Lemon parser and running into a methodological problem
> that
> > I
> > wanted to ask the user base about. Is there a mailing list or forum
> > specifically for Lemon, or is this it? :)
> >
> > Thanks,
> > -Chris
>
> There is no mailing list specifically for lemon. Some of us are
> familiar to various degrees with lemon, so feel free to ask here.
> Though I must say, lemon questions tend languish for a while before
> someone replies. Don't be afraid to bump your own message if it isn't
> answered. I think it's safe to say that most sqlite users aren't
> initimately familiar with lemon.
>
> RW
>
> Ron Wilson, Engineering Project Lead
> (o) 434.455.6453, (m) 434.851.1612, www.harris.com
>
> HARRIS CORPORATION | RF Communications Division
> assuredcommunications(tm)
> _______________________________________________
> sqlite-users mailing list
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>
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