[augeas-devel] Fixing ambiguous iteration errors

[Tom Limoncelli]

I'm trying to write a lens to parse Xen configuration files
(xend-config.sxp) which is a very lisp-like format "(key value) (key2
(key value))" and I'm getting nowhere.  I've learned a lot from
working through the tutorials.  However I've also realized that I
don't remember enough from my parsing and compilers class back in
college :-).  (it was more than 20 years ago)

If you don't mind some noob questions....

1. The Schema Tutorial (http://augeas.net/docs/writing-schemas.html)
doesn't explain what |=| means.  I assume it is just a "pointer" to
where the ambiguity starts.  Clarification, please?

2.  I keep getting "ambiguous iteration" errors.  Unsurprisingly, I
remember this being difficult for me to grasp when I was in college
doing homework assignments in Yacc.  Is there a technique for
diagnosing and fixing these?  A rule of thumb for avoiding them?

The tutorials are great in that they go through the debugging process
but they don't explain the thinking that leads to the changes made to
fix the bugs as they are found.  I'd be glad to work with someone to
improve them.

Thanks,
Tom Limoncelli

P.S.  As an example, the error I'm dealing with right now is:

$ augparse -I. tests/test_xendconfsxp.aug Syntax error in lens
definition./xendconfsxp.aug:25.0-.44:Failed to compile
lns./xendconfsxp.aug:25.10-.44:exception: ambiguous iteration
Iterated regexp: /\\([\t\n ]*[0-9A-Z\\a-z-]+[\t\n ]+[^\t\n ]+[\t\n
]*\\)|[\t ]*#[\t ]*([^\t\n ].*[^\t\n ]|[^\t\n ])[\t ]*\n|[\t ]*\n/
 '(A\nA)#)\n' can be split into      '(A\nA)|=|#)\n'
     and      '(A\nA)#)|=|\n'
    Iterated lens: ./xendconfsxp.aug:25.12-.41:
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