[ragel-users] One question.

Matt Mongeau halogenandtoast at gmail.com
Tue Mar 29 20:44:04 UTC 2011

So I had to look this one up too, but from the documentation:

6.7 Parsing Recursive Language Structures
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 implement
the recursive parts using manual coding techniques. This often works in
cases where the recursive
structures are simple and easy to recognize, such as in the balancing of
One approach to parsing recursive structures is to use actions that
increment and decrement
counters or otherwise recognize the entry to and exit from recursive
structures and then jump to
the appropriate machine defnition using fcall and fret. Alternatively,
semantic conditions can
be used to test counter variables.
A more traditional approach is to call a separate parsing function
(expressed in the host lan-
guage) when a recursive structure is entered, then later return when the end
is recognized.

Hope this helps.

On Tue, Mar 29, 2011 at 4:15 PM, Gordeev Vladimir <
gordeev.vladimir.v at gmail.com> wrote:

>  Hi everyone,
> Actually I just started to work with Ragel and probably don't understand
> right the concept.
> I'm trying to write parser for toy programming language. All was ok, before
> I mess with recursive
> definitions.
> I want to read lisp-like expressions, e.g. ((((one)) (two)) three), and try
> to write recursive definition for it.
> the same at gist: https://gist.github.com/893142
>  %%{
>   machine lisp;
>   integer = '-'? . ('0'|[1-9][0-9]*);
>   string = '"' . (any - '"') . '"';
>   list = '(' . (integer|string|list)* . ')';
>   main := list;
> }%%
> %% write data;
> %% write init;
> %% write exec;
> So I got following error:
>     test.rl:7:32: graph lookup of "list" failed
> So, the question is: How to define parser for such language.
> Yea, sorry my bad English.
> _______________________________________________
> ragel-users mailing list
> ragel-users at complang.org
> http://www.complang.org/mailman/listinfo/ragel-users
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