On Jul 23, 12:43 pm, [EMAIL PROTECTED] (Eddie Corns) wrote: > Paul McGuire <[EMAIL PROTECTED]> writes: > >On Jul 23, 5:53 am, [EMAIL PROTECTED] (Eddie Corns) wrote: > >> Wolfgang Strobl <[EMAIL PROTECTED]> writes: > >> >few of James Gimple's snippets from "Algorithms in SNOBOL4" > >> >(->http://www.snobol4.org/) as an exercise using that library might help > >> >to get a better appreciation. Perhaps I'll try, eventually ... > > >> I never noticed them or the PDF of the book there before. Some Friday > >> afternoon reading for sure. > > >> Personally I hope to get more to time to look at a combination of Lua and > >> PEGs (http://en.wikipedia.org/wiki/Parsing_expression_grammar) for my > >> parsing > >> needs. > > >> Eddie > >If you get a chance to look at pyparsing, I'd be interested in your > >comments. The PEG page and the SNOBOL implementation have many > >similar concepts with pyparsing (or is it the other way around?). > > It's on my list of things to get round to. > > I think what I'm really after though is a parsing DSL. I only did only one > fairly small project in SNOBOL but I was impressed at the ease with which I > could express the problem (some googling suggested that many end users found > the same). I guess I want SNOBOL embedded in a modern language with scoping > etc. Python is antithetical to (this class of) DSLs (IMHO) :( > > Probably what I really need is parser combinators in Haskell or maybe camlp4 > or some such exotica but unfortunately I've never heard of them. > > Eddie- Hide quoted text - > > - Show quoted text -
I have had pyparsing users refer to pyparsing as an in-Python DSL, and others make comparisons between pyparsing and Parsec (monadic combinator in Haskell). I'm not sure why you would say this approach is antithetical to Python - the builtin support for operator overloading, __call__, __len__, __nonzero__(soon to be __bool__), __set/getattr__, etc. permit you to impart quite a bit of expressive behavior to your parsing classes. What I tried to do with pyparsing was to emulate Python's builtin container classes and object instances with the results that get returned from invoking a parser, so that the after-parsing work would feel natural to established Python users. If you want to just see some existing BNF's implemented in pyparsing, you can view them online at the pyparsing wiki. Here are some representative examples: http://pyparsing.wikispaces.com/space/showimage/simpleSQL.py http://pyparsing.wikispaces.com/space/showimage/fourFn.py http://pyparsing.wikispaces.com/space/showimage/jsonParser.py -- Paul -- http://mail.python.org/mailman/listinfo/python-list
