Re: [boost] Formal Review: The Spirit Parser Framework.

From: Vladimir Prus (ghost_at_[hidden])
Date: 2002-10-16 05:30:17

John Maddock wrote:
 > The formal review for the Spirit Parser Framework begins today, and runs
 > until the end of Sunday 20th October.

I've tried to apply Spirit to read a certain structure and have several
comments/question. This is not a review yet, I hope to make one later.

1. I tried for some time to figure out what header I should include from
documentation, and found that only from example linked from the bottom
of "quick start" section. Maybe, this can be said in more visible place.

2. I guess namespace for spirit will be changed to "boost::spirit"?

3. I have problems with parsing streams. As I understand, Spirit
requires forward iterators, and therefore can't work with
istream_iterator or istreambuf_iterator directly. It means that if I
need to parse *part* of stream, I'm in trouble. Consider these rules:

      rule<> element = ch_p('(') >> ( int_p % ch_p(',') ) >> ch_p(')');
      rule<> r = ch_p('[') >> (element % ch_p(',')) >> ch_p(']');

To parse 'r' with Spirit, I'd have to extract part of input
corresponding to 'r' and then call 'parse' rule. In this particular
case, this might be not very hard, but it's bad in general. Probably, a
wrapper around istream may be written, which will provide forward
iterators, getting additional symbols from istream as required. Hmm..
not sure what happens if you read more characters that belong to 'r'.

4. The section called "scanner business" is hidden to much. For example,
I did not read the entire documentation completely, but started
experimenting, and run in the problem described in that section. Maybe,
this should be noted in "Quick start". BTW, I'd prefer quick start to
contain two *minimal examples* as *inline test*. The first would create
rule in 'parse' invocation and the second would use 'grammar' and
reference "scanner business".

5. Say I'm parsing a list of pairs, something like:

       ch_p('[') >>
        (
            ( ch_p('(') >> int_p[??] >> ch_p(',')
		    >> int_p[??] >> ch_p(')') )
               %
               ch_p(',')
          )
        >> ch_p(']')

   How do I store those pairs, for example, in map? Does semantic action
for the first int should store the date in some variable, and semantic
action for the second it should read it? IOW, can semantic action for
the second int directly access part of string that corresponds to the
first int?

6. If I have to store first int somewhere, then where? The natural place
for this would be grammar, but 'definition's ctor gets constant
reference to the grammar. Probably, closures with help with 5 and 6, but
   I don't yet see how to apply them.

7. Regarding closures. They, in particular, allow to assign semantic
values to rules. Is it possible to assign different semantic values to
different rules in a grammar? I.e. "expression" would have only value,
while "function" would have much more attributes?

- Volodya