There seems to be a gazillion regular expression libraries. Most of them
only work on text, but I wanted something that also worked on arbitrary
sequences of data ( this is useful, for instance, in building parse trees
from token lists ). This is possible, I think, using the Spirit library from
Boost, but the syntax and complexity again is too much for me. I almost
finished the YARD ( yet another recursive descent ) parser which is a really
lightweight truly generic regex parser (and runs like a bat out of hell).
Anyway, the syntax is essentially as follows:
You define rules as follows:
typedef CharRange_parser<'a', 'z'> LowerCaseLetter_parser;
typedef CharRange_parser<'A', 'Z'> UpperCaseLetter_parser;
typedef CharRange_parser<'0', '9'> Number_parser;
typedef re_or<LowerCaseLetter_parser, UpperCaseLetter_parser> Letter_parser;
typedef re_or<Letter_parser, Char_parser<'\''> > WordChar_parser;
typedef re_plus<WordChar_parser> Word_parser;
typedef re_or<Letter_parser, Char_parser<'_'> > IdentFirstChar_parser;
typedef re_or<IdentFirstChar_parser, Number_parser> IdentOtherChar_parser;
typedef re_and<IdentFirstChar_parser, re_star<IdentOtherChar_parser> >
Ident_parser;
Then you hand them to a tokenizer as follows:
int main ()
{
nBufSize = GetFileSize(sFileName);
pBuf = static_cast<char*>(calloc(nBufSize, 1));
ifstream f;
f.open(sFileName);
f.read(pBuf, nBufSize);
f.close();
Tokenizer<Word_parser> tknzr;
tknzr.Parse(pBuf, nBufSize);
OutputTokens(tknzr.Begin(), tknzr.End());
free(pBuf);
getchar();
return 0;
}
A tokenizer in this case is really simple:
template<typename Parser_T>
struct Tokenizer {
void Parse(char* pText, int nSize)
{
ParseInputStream stream(pText, nSize);
while (!stream.AtEnd()) {
int index = stream.GetIndex();
if (Rules_T::Accept(stream)) {
mTkns.push_back(Token(index, stream.GetIndex()));
}
stream.GotoNext();
}
}
TokenIter Begin() { return mTkns.begin(); }
TokenIter End() { return mTkns.end(); }
private:
TokenList mTkns;
};
What I want to know is this obvious to programmers how it works and how to
use it? Is the verbosity acceptable? Also, would it interest people more if
I showed some benchmarks comparing it to other libraries?
TIA
--
Christopher Diggins
http://www.cdiggins.com
http://www.heron-language.com
