On Tue, Sep 23, 2014 at 3:20 PM, Thierry Goubier <thierry.goubier@gmail.com> wrote:

2014-09-23 13:57 GMT+02:00 Udo Schneider <udo.schneider@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.schneider@homeaddress.de
<mailto:udo.schneider@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.schneider@homeaddress.de
�� <mailto:udo.schneider@homeaddress.de>
�� <mailto:udo.schneider@__homeaddress.de
�� <mailto:udo.schneider@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.schneider@homeaddress.de
�� <mailto:udo.schneider@homeaddress.de>
�� <mailto:udo.schneider@__homeaddress.de
�� <mailto:udo.schneider@homeaddress.de>>
�� <mailto:udo.schneider@
�� <mailto:udo.schneider@>__homead__dress.de <http://homeaddress.de>

�� <mailto:udo.schneider@__homeaddress.de
�� <mailto:udo.schneider@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.schneider@homeaddress.de
�� <mailto:udo.schneider@homeaddress.de>
�� <mailto:udo.schneider@__homeaddress.de
�� <mailto:udo.schneider@homeaddress.de>>
�� <mailto:udo.schneider@
�� <mailto:udo.schneider@>__homead__dress.de <http://homeaddress.de>
�� <mailto:udo.schneider@__homeaddress.de
�� <mailto:udo.schneider@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