3 ms·

Honest question: why hasn't anyone come up with a system for "context-free" expressions?

• silentbicycle 16y ago
  There are plenty of tools for dealing with context-free grammars. I'm not sure what distinction you're making by referring to context-free expressions. I like ocamllex + ocamlyacc, or LPEG for lighter stuff. Flex and yacc are ok, but C is really not my first choice for string-heavy stuff.
  • nerfhammer 16y ago
    "context-free expression" = to context-free grammars as regular expression is to regular grammars
    • silentbicycle 16y ago
      I'm still not 100% sure, but I think LPEG (http://www.inf.puc-rio.br/~roberto/lpeg/lpeg.html http://www.inf.puc-rio.br/~roberto/lpeg/lpeg.html) fits the bill. Ignore for now that it's a Lua library - there's nothing Lua-specific about its underlying design. There's a great paper (http://www.inf.puc-rio.br/~roberto/docs/peg.pdf http://www.inf.puc-rio.br/~roberto/docs/peg.pdf) about it. It's a PEG-based string pattern-matching engine. It can build parse trees out of strings or execute code on portions of them just as easily as it can validate their structure, though in the documentation that's a bit of an afterthought. It's also very fast, and integrates as nicely with Lua as regular expressions do in Perl. It's also just a smallish C library that could be (maybe already has) been ported to Python / Ruby / whatever.