2014-09-23 13:57 GMT+02:00 Udo Schneider <udo.schnei...@homeaddress.de>:
> > yeap noway I compare Regex with PettitParser. I will probably give a > > PettitParser a try, because I try to parse Pharo syntax to Python, I > > want now to parse Pharo classes to python class and that will be a > > nightmare with regex, so time to give PettitParser a serious try. > Without wanting to go too deep into theory... Parsing Pharo or Python > would definitely need a Chromsky Type 2 language (Context free grammar). So > you'd be out of luck parsing Smalltalk or Python code with Regular > Expressions (Chromsky Type 3) only - except maybe for some very simple > expressions. > Confirmed in even a better way: given how convoluted and hacky is writing a full Python Parser, it is probably not even a Context Free Grammar. That is: the Python grammar is LALR which is a subset of Context Free Grammar (but already more than a type 3 Chomsky grammar), but the Lexer is a fair bit more than usual (dedent tokens come to mind; special handling of end of lines as well). I think you need a fair bit of special magic in PetitParser to parse Python. Luckily, Python is well documented in that regard. Thierry > > CU, > > Udo > > > On 23.09.14 13:35, kilon alios wrote: > >> yeap noway I compare Regex with PettitParser. I will probably give a >> PettitParser a try, because I try to parse Pharo syntax to Python, I >> want now to parse Pharo classes to python class and that will be a >> nightmare with regex, so time to give PettitParser a serious try. >> >> On Tue, Sep 23, 2014 at 1:10 PM, Udo Schneider >> <udo.schnei...@homeaddress.de >> <mailto:udo.schnei...@homeaddress.de>> wrote: >> >> > I have not used PettitParser yet, looks powerful but I find it a bit >> > weird in design. On the other hand regex is quite ugly and >> understanding >> > complex regex a pain. >> I normally encounter two issues with RegExps: >> >> 1) The syntax between different apps/libs/frameworks differs >> sligtly. Esp. for character classes or greediness. This drove me >> crazy more than one time. >> 2) Often enough I realize (while developing the RegExp) that I need >> something more capable than a Chomsky Type 3 parser (which RegExps >> are in a way). So I have to use "a bigger gun" - e.g. PetitParser. >> >> CU, >> >> Udo >> >> >> On 23.09.14 10:15, kilon alios wrote: >> >> it reminds a lot of Kent's Beck Smalltalk Practice Patterns where >> it >> removes all ifs and replaces them with regular unary messages . >> It is >> definitely an elegant way of coding making the code just flow. >> >> I have not used PettitParser yet, looks powerful but I find it a >> bit >> weird in design. On the other hand regex is quite ugly and >> understanding >> complex regex a pain. >> >> On Tue, Sep 23, 2014 at 11:07 AM, Udo Schneider >> <udo.schnei...@homeaddress.de >> <mailto:udo.schnei...@homeaddress.de> >> <mailto:udo.schneider@__homeaddress.de >> <mailto:udo.schnei...@homeaddress.de>>> >> wrote: >> >> > just as it is black magic for me now :D >> The nice thing about this approach is the fact that it "just" >> piggybacks the normal Smalltalk message sending. So you can >> step >> through it using the Debugger - it's Smalltalk all the way >> down. >> >> I still remember my first shock when (having no formal >> background on >> parsing theory at that time) I saw the parsing tables >> generated by >> T-Gen. Of course it was Smalltalk ... but understanding >> those tables >> was a nightmare. >> >> PetitParser is the gold standard here IMHO. It is able to >> parse >> arbitrary input (compared to my block expressions only). >> And you can >> still use the Debugger to step through the parsing process >> *and >> still understand what's going on!* >> >> CU, >> >> Udo >> >> On 23.09.14 09:54, kilon alios wrote: >> >> just as it is black magic for me now :D >> >> At least I get the general feeling. I am new to parsing >> too, so >> far I >> have only played with regex parsing. Not the most >> smalltalkish >> way but >> it works well so far. >> >> On Tue, Sep 23, 2014 at 9:39 AM, Udo Schneider >> <udo.schnei...@homeaddress.de >> <mailto:udo.schnei...@homeaddress.de> >> <mailto:udo.schneider@__homeaddress.de >> <mailto:udo.schnei...@homeaddress.de>> >> <mailto:udo.schneider@ >> <mailto:udo.schneider@>__homead__dress.de <http://homeaddress.de> >> >> >> <mailto:udo.schneider@__homeaddress.de >> <mailto:udo.schnei...@homeaddress.de>>>> >> wrote: >> >> Hi Estaban, >> >> I think the first time I saw this pattern was in >> ReStore on >> Dolphin >> Smalltalk. I didn't understand it's implementation >> back then. I >> assume that it's similar to what I described >> though. But >> having a >> Smalltalk block automagically creating the >> equivalent SQL >> SELECT >> expression was like black magic at that time :-) >> >> CU, >> >> Udo >> >> >> >> >> On 23.09.14 04:15, Esteban A. Maringolo wrote: >> >> Excellent article. >> >> I think GLORP uses a similar technique to >> setup its >> expressions, and >> also have issues with #and:/#or: selectors due >> to >> inlining, so >> it uses >> AND:/#OR: instead. >> >> Regards! >> >> Esteban A. Maringolo >> >> pd: Your blog and it's choosen topic made me >> remember >> http://use-the-index-luke.com/ >> >> 2014-09-22 20:48 GMT-03:00 Udo Schneider >> <udo.schnei...@homeaddress.de >> <mailto:udo.schnei...@homeaddress.de> >> <mailto:udo.schneider@__homeaddress.de >> <mailto:udo.schnei...@homeaddress.de>> >> <mailto:udo.schneider@ >> <mailto:udo.schneider@>__homead__dress.de <http://homeaddress.de> >> <mailto:udo.schneider@__homeaddress.de >> <mailto:udo.schnei...@homeaddress.de>>>>__: >> >> >> All, >> >> I just finished a blog entry. It shows how >> to use >> Smalltalk >> blocks as parsers/translators. E.g. >> translating a Block >> >> [:customer | (customer joinDate >> year is: Date >> today year)] >> >> into an SQL-like String >> >> (YEAR(customers.joinDate) = 2014) >> >> The SQL stuff is just an example - you can >> create >> nearly any >> output. >> >> Check out >> http://readthesourceluke.__blo____gspot.de/2014/09/block-___ >> ___translators-parsing-magic.html >> <http://blo__gspot.de/2014/09/block-____translators-parsing- >> magic.html> >> >> <http://blogspot.de/2014/09/__block-__translators-parsing-__ >> magic.html >> <http://blogspot.de/2014/09/block-__translators-parsing- >> magic.html>> >> >> >> <http://readthesourceluke.__bl__ogspot.de/2014/09/block-____ >> translators-parsing-magic.html >> <http://blogspot.de/2014/09/block-__translators-parsing- >> magic.html> >> >> <http://readthesourceluke.__blogspot.de/2014/09/block-__ >> translators-parsing-magic.html >> <http://readthesourceluke.blogspot.de/2014/09/block- >> translators-parsing-magic.html>__>__> >> >> Maybe that's old stuff for some of you - >> but I hope >> it's >> interesting for some at least :-) >> >> Comments and feedback appreciated. >> >> CU, >> >> Udo >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> >> > > >
