I am trying to write a parser which skipps white space and C, Java style
comments. To get familiar with spirit, I did some experiments, here is a
question.
First, I write a simple grammar to accept some non-white space chars.
////////////////////////////////////////////////////////////////////////////
////
struct FOO_GRAMMAR : public grammar
{
template <typename ScannerT>
struct definition
{
typedef rule<ScannerT> rule_t;
definition(ABNF_GRAMMAR const & self)
{
r_LETTER =
range_p('a','z')
| range_p('A','Z')
| '.';
r = (+r_LETTER);
}
rule_t r, r_LETTER;
rule_t const& start() const { return r; }
};
};
////////////////////////////////////////////////////////////////////////////
////
I used FOO_GRAMMAR with space_p as skip parser:
////////////////////////////////////////////////////////////////////////////
//
FOO_GRAMMAR g;
std::string line = "This is a test parser.";
parse_info<> info = parse(line.begin(),line.end(), g, space_p);
////////////////////////////////////////////////////////////////////////////
////
This works perfectly.
Then, I tried to wrap the skip parser in a skip grammar, since eventually I
need a more complicated parser. So I wrote the skip grammar as:
////////////////////////////////////////////////////////////////////////////
///
struct SKIP_GRAMMAR : public grammar
{
template <typename ScannerT>
struct definition
{
typedef rule<ScannerT> rule_t;
definition(SKIP_GRAMMAR const & self)
{
rule_t r_SKIP = space_p;
}
rule_t r_SKIP;
rule_t const& start() const { return r_SKIP; }
};
};
/////////////////////////////////////////////////////////////////////////
I tried to parse the same sentence as before:
///////////////////////////////////////////////////////////////////////////
FOO_GRAMMAR g;
SKIP_GRAMMAR skip;
std::string line = "This is a test parser.";
parse_info<> info = parse(line.begin(),line.end(), g, skip);
//////////////////////////////////////////////////////////////////////////
This time the parsing failed.
Can anyone tell me why? I thought grammars are just like rules.
And any suggestion on building a parser skipping certain pattern? I just can
figure it out by reading the doc.
Thank you.
Jia (Jay) Pu
Software Engineer
LumenVox LLC
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Anytime a linguist leaves the group the recognition rate goes up.
--Fred Jelinek (then of the IBM speech group) (1988)
