[ragel-users] Machine definitions that depend on each other

Adrian Thurston thurs... at cs.queensu.ca
Wed May 16 00:13:05 UTC 2007


In general, Ragel cannot handle recursive structures because the grammar
is interpreted as a regular language.

However, depending on what needs to be parsed it is sometimes practical
to manually implement the recursive part using fcall/fret. The trick is
to think of these as function calls and to mimic a recursive descent
parser. To balance parentheses you can often use counters and fgoto.
Conditions are also a possibility. Look in test/cond6.rl for an example.


chrsan wrote:
> Hi!
> I'm working with Ragel for the first time, implementing a CSS scanner/
> parser.
> I've run into trouble having machine definitions that depend on each
> other. In the following
> example term refers to function which in turn refers to expr that
> refers to term.
> What's the best way to solve this in Ragel?
> I haven't come up with a way to solve this by rearranging the
> definitions.
> function = ident '(' s* expr ')' s*;
> term = ( ( ( unary_operator? ( unary_term | num ident ) ) | string |
> ident | uri ) s* ) | hexcolor | function;
> operator = ( '/' | ',' ) s*;
> expr = term ( operator? term )*;
> Thanks in advance,
> Christer Sandberg
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