| === h\h is now known as haraldh | ||
| ion | keybuk: Feel like merging my mountall changes? :-) I could rebase the patch set on to the current mountall source package later today, but there are probably no conflicts. | 13:21 |
|---|---|---|
| Keybuk | ion: am going to merge after alpha 6 is out | 13:22 |
| ion | Alright | 13:22 |
| pocek | Hi | 19:58 |
| sadmac2 | hello | 19:59 |
| pocek | How's upstart 1.0 going? I watched fosdem video and it seems really promising :) | 20:05 |
| sadmac2 | its going' | 20:05 |
| sadmac2 | pocek: are you on the mailing list? | 20:09 |
| pocek | Just subscribed | 20:12 |
| sadmac2 | pocek: well that's the place to be | 20:12 |
| sadmac2 | I'll probably shoot another braindump towards scott tonight | 20:13 |
| Keybuk | \o/ | 20:14 |
| sadmac2 | Keybuk: celebrating my braindump or have you done wonders? | 20:15 |
| Keybuk | celebrating your brain dumps | 20:16 |
| Keybuk | I like them | 20:16 |
| sadmac2 | sweet | 20:16 |
| Keybuk | for a start, they help me actually work out what *I* mean sometimes :p | 20:16 |
| Keybuk | plus you have lots of ideas | 20:16 |
| sadmac2 | Keybuk: I got a bit sidetracked last night in my coding. Long story short libnih is about to grow a non-deterministic RE language parser to replace nih_config :) | 20:16 |
| sadmac2 | Keybuk: bison was inadequate, so I'm writing us our own. | 20:16 |
| Keybuk | heh | 20:17 |
| Keybuk | I'm clearly rubbing off on you ;) | 20:17 |
| ion | :-) | 20:17 |
| Keybuk | "why use this pre-canned library when I COULD WRITE MY OWN!" :p | 20:17 |
| ion | sadmac: Have you looked at PEGs? | 20:18 |
| ion | http://treetop.rubyforge.org/ as an example project implementing PEG. | 20:18 |
| ion | They have some pros and some cons. | 20:18 |
| sadmac2 | ion: I spent a good few hours trying to get my hands on any parser generators I could find. Didn't find those. | 20:22 |
| sadmac2 | ion: the big thing we need is a non-deterministic lexer. For example: "start on start". The same token has two different meanings in that stanza. | 20:23 |
| sadmac2 | Its a keyword, and then later its an unquoted string. | 20:24 |
| ion | PEG should handle that fine | 20:24 |
| ion | Without any extra effort. | 20:24 |
| sadmac2 | ion: the other thing I wanted (more of a nice-to-have) is expressions that take arguments. Its good for things like this: | 20:25 |
| sadmac2 | opstring(SEP) ::= event SEP OPERATOR SEP event | 20:25 |
| sadmac2 | on_opstring ::= opstring(NONBREAKING_SPACE) | 20:26 |
| sadmac2 | event ::= event_spec | '(' opstring(BREAKING_SPACE) ')' | 20:27 |
| ion | Please give an example of a chunk to be parsed by that. | 20:27 |
| sadmac2 | the being-nested-makes-linebreaks-ok thing is really annoying in bison | 20:27 |
| ion | Ah | 20:27 |
| sadmac2 | ion: surely. "start on a and (b or \n c) \n start on a and b or \n c" | 20:28 |
| ion | Yeah, got it | 20:28 |
| sadmac2 | ion: the \ns are linebreaks | 20:28 |
| sadmac2 | ion: the second line there should be an error | 20:28 |
| sadmac2 | ion: the first should be fine | 20:28 |
| sadmac2 | its less of a pain to do conventionally when you don't have big chunks of identical handler code for each version of opstring | 20:29 |
| sadmac2 | that grammar was kinda fudgy | 20:30 |
| sadmac2 | opstring(SEP) ::= event | opstring(SEP) SEP OPERATOR SEP opstring(SEP) | '(' opstring(BREAKING_SPACE) ')' | 20:32 |
| sadmac2 | on_opstring ::= opstring(NONBREAKING_SPACE) | 20:32 |
| sadmac2 | much better. | 20:32 |
| sadmac2 | BNF is hard, lets go shopping | 20:32 |
| sadmac2 | ion: implementing these can't be easy, and ruby isn't a good libnih dependency :) | 20:41 |
| ion | As i said, it’s just an example implementation. One is free to implement PEG without such dependencies. | 20:42 |
| sadmac2 | ion: yeah, I just wonder what it would take to do in C :) | 20:46 |
| sadmac2 | ion: right now the plan is just to use C syntax and express it that way. | 20:46 |
| sadmac2 | with hopes of then bootstrapping the specification of a better grammar through that later on. | 20:49 |
| ion | Extending e.g. Treetop’s ‘rule’ element with parameters (as you described) would be very natural in fact. If one is to implement PEG in C, passing the separator as a parameter wouldn’t be the hard part. :-) | 20:50 |
| ion | Pseudo-treetopish-code: | 20:51 |
| ion | On a second thought, i’ll write this to pastebin. Moment. | 20:51 |
| ion | Something like http://pastebin.com/f79d84635 | 20:57 |
| sadmac2 | ion: I'm so used to people bending ruby into dsls that I keep trying to think how this still constitutes valid ruby :) | 20:58 |
| ion | PEG consumes input greedily, just like a regexp, without a need for separate tokenization. PEG can be thought of as an extended regexp that supports giving names to chunks and calling them by names (and recursion comes with that). | 20:59 |
| ion | That’s not Ruby. That’s Treetop grammar syntax. | 20:59 |
| sadmac2 | ion: yeah | 20:59 |
| ion | Say, begin with a plain regexp: | 21:04 |
| ion | hello\s+[a-zA-Z0-9]+ | 21:04 |
| ion | Give it a name: | 21:04 |
| ion | hello_stanza := hello\s+[a-zA-Z0-9]+ | 21:04 |
| ion | Split it to parts and give them names: | 21:05 |
| ion | hello_stanza = 'hello' whitespace name; whitespace := \s+; name := [a-zA-Z0-9]+ | 21:05 |
| ion | And implement support for recursion. There’s your basic PEG parser. | 21:05 |
| ion | Just a regexp engine extended a bit. | 21:05 |
| sadmac2 | ion: sounds nice. | 21:06 |
| sadmac2 | ion: I may do that. | 21:06 |
| sadmac2 | ion: I could probably extend glibc regexen to do most of it for me too | 21:06 |
| ion | And as for precedence, it’s greedy just like regexps: the first matching tree is the one it picks. | 21:07 |
| ion | Want anything in parenthesis to have precedence over an and expression, and that to have precedence over an or expression? Give them in that order: | 21:08 |
| ion | event_spec := '(' event_spec ')' | event_spec sep 'and' sep event_spec | event_spec sep 'or' sep event_spec | event; | 21:08 |
| ion | or something along those lines. | 21:08 |
| ion | The regexp engine looks at the next character. Is it '('? Nope? Then look at the next alternative. Just like a plain regexp such as /\(foo\)|alternative|another/ | 21:09 |
| ion | PEG does have some disadvantages: http://en.wikipedia.org/wiki/Parsing_expression_grammar#Disadvantages | 21:10 |
| sadmac2 | ion: searching the fedora repos for peg gives me every mpeg and jpeg tool or library ever written | 21:21 |
| ion | http://piumarta.com/software/peg/ | 21:21 |
| sadmac2 | ion: I was just about to link you the same thing | 21:21 |
| ion | Search for \<peg\> or \bpeg\b, depending on the regexp dialect of rpm or whatever. :-P | 21:21 |
| ion | (No PEG results in Ubuntu, though.) | 21:22 |
| sadmac2 | ion: this looks new, and reeks of next months abandonware | 21:23 |
| ion | He has bothered to write an extensive manual, that tells something. :-) http://piumarta.com/software/peg/peg.1.html | 21:23 |
| sadmac2 | Keybuk: care to weigh in with preferences? | 21:24 |
| === robbiew is now known as robbiew-afk | ||
| === sadmac_ is now known as sadmac | ||
| === robbiew-afk is now known as robbiew | ||
| === robbiew is now known as robbiew-afk | ||
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