World: r3wp
[Parse] Discussion of PARSE dialect
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BrianH 7-Nov-2008 [2920] | That page is it unless we get more suggestions. We haven't decided what makes the cut yet even for those. |
Steeve 7-Nov-2008 [2921x2] | hum (i have to be a little bit rude), i just read your response on rebol.net about the opportunity to turn or not return into a more genralized EMIT functions (as i proposedl). I will not discuss about the difficulty to implement that idea (i don't have the sources). But what i can say, is that a COLLECT behaviour will be more usefull than all return break/return stuffs u posted. Have you inspected scripts in Rebol.org recently ? If u had done, you would see that many coders use parsing to collect data. The problem Graham, is that when i read your arguments, i have the unpleasant impression that your are alone to decide if an idea is bad or good. The narrow minded sentence " Incorporating COLLECT and KEEP into PARSE is both unnecessary and doesn't help at all for building hierarchical structures" suggest that you had not widely used parse in your code. I don't think you are the best people here to made these choices. Many script contributors on Rebol.org have made some masterfull piece using parse (not you). So when you reject an idea you should be more sensitive with this simple fact: many poeple here have an equal or better experience whit parsing than you. |
by the way, many people have proposed the idea you posted in the wiki (just read some scripts on Rebol.org) you should be a little bit less quick to credit you of ideas that are here since several years. | |
Anton 7-Nov-2008 [2923] | (Steeve, I think you are addressing BrianH, not Graham.) |
Steeve 7-Nov-2008 [2924x3] | really ? |
oh my... | |
yes it talk to BrianH, what do u mean ? | |
Anton 7-Nov-2008 [2927] | You wrote above, "The problem Graham, is that when i read your arguments..." |
Steeve 7-Nov-2008 [2928x2] | oh i see, my Apologies to Graham |
I was a little upset when I wrote it ;-) | |
Pekr 8-Nov-2008 [2930x2] | uhmm, well, Steeve, as for me, if my proposal is going to be implemented, I don't care if I am credited or not. Because - parser REPs are floating here or there for some 8 years maybe :-) As for BrianH and his judgements - he might not be better in parse than others, but I would not try to upset him - BrianH is our guru here. Along with Gabriele, Cyphre, and after loss of Ladislav, he is one of the most skilled rebollers. I think that his intention is to help REBOL being better. He might be also the one, who will bring JIT or compiler in the future, and he understand consequences of what he suggests ... |
I have to ask - what ppl are you referring to, regarding rebol.org? Why they are not here, or posting to blog? BrianH might be quick in his decision, because Carl selected him to collect the ideas, so let's forgive him a little bit of guru behaviour :-) And in the end, it is Carl who decides, if REP is going to be implemented or not. If you have another pov on some REP, why not to talk about it here, where more ppl can judge? | |
BrianH 8-Nov-2008 [2932] | I'm not angry, promise :) |
Pekr 8-Nov-2008 [2933] | :-) OK |
BrianH 8-Nov-2008 [2934x4] | Nonetheless, I think I need to apologize to Steeve, especially in the original sense of explanation. |
I am the editor of the PARSE proposals. It was decided that I perform this role because Carl is focused on the GUI work right now and someone qualified had to do it. With Carl busy and Ladislav not here, I am the one left who has the most background in parsing and the most understanding of what can be done efficiently and what can't. When the PARSE REPs of old were discussed, I was right there in the conversation and the originator of about half of them, mostly based on my experience with other parsers and parser generators. Because of this I am well aware of the original motivation behind them, and have had many years to think them through. It's just head start, really. I am also the author of the current implementation of COLLECT and KEEP, based on Gabriele's original idea, which was a really great idea. It is also really limited. Collecting information and building data structures out of it is the basic function that programming languages do, and something that REBOL is really good at. I am not in any way denigrating the importance of building data structures. I certainly did not mean to imply that your appreciation of that important task was in any way less important. The role of an editor is not just to collect proposals, but to make sure they fit with the overall goal of the project. This sometimes means rejecting proposals, or reshaping them. This is not a role that I am sorry about - someone has to do it to make our tool better. We are not Perl, this is not anything goes, we actually try to make the best decisions here. I hate to seem the bad guy sometimes, but someone has to do it :( PARSE is a portion of REBOL that is dedicated to a particular role. It recognizes patterns in data, extracts some of the data, and then calls out to the DO dialect to do something with the data. It doesn't really do anything to the data itself - everything happens in the DO dialect code in the parens. It is fairly simple really, and from carefully designed simplicity it gets a heck of a lot of power and speed. That is its strength. The thing that a lot of people don't remember when making improvements to a dialect like PARSE is that PARSE is only one part of REBOL. If something doesn't go into PARSE, it can go into another part of REBOL. We have to consider the language as a whole when we are doing things like this. Here is the overall rationale for the PARSE dialect proposals: - All new features need to be simple to explain and use, and fast at runtime. - A good feature would be one of these: - An extremely powerful enhancement of PARSE's language recognition. - A fix to a design flaw in an existing feature, or a compatibility fix. - A serious improvement to a sufficiently common use case, or common error. The reason I didn't want to put COLLECT and KEEP into PARSE is because it is a small part of a much bigger problem that really needs a lot of flexibility. Different structure collection and building situations require different behavior. It just so happens that the DO dialect is much better suited to solving this particular problem than the PARSE dialect is. Remember, PARSE is a native dialect, and as such is rather fixed. There are some PARSE proposals that make parse actually do something with the data itself: CHANGE, INSERT and REMOVE. We were very careful when we designed those proposals. In particular, we wanted to provide the bare minimum that would be necessary to handle some very common idioms that are usually done wrong, even by the best PARSE programmers. Sometimes we add stuff into REBOL that is just there to solve a commonly messed up problem, so that a well debugged solution would be there for people to choose instead of trying to solve it again themselves, badly. (This is why the MOVE function got added to R3 and 2.7.6, btw.) Even with that justification those features might not make it into PARSE because they change the role of PARSE from recognition to modification. I have high hopes, though. Another proposal that might not make it into PARSE is RETURN. RETURN is another ease-of-use addition. In particular, the thing it makes easy is stopping the parse in the middle to return some recognized information. However, it changes the return characteristics of PARSE in ways that may have unpredictable results, and may not have enough benefit. The proposal that has a better chance of making it is BREAK/return, though I'd like to see both (we can hope, right?). Most of the REPs from Gabriele's doc have been covered. Most of them have been changed because we have had time in the last several years to give them some thought; the only unchanged ones are NOT and FAIL, so far. Some have been rejected because they just weren't going to work at all (8 and 12). THROW and DO are still under discussion - the proposals won't work as is, but the ideas behind them have merit. The rest have been debated and changed into good proposals. Note that the DO proposal would be rejected outright for R2, but R3's changes to word binding make it possible to make it safe (as figured out during a conversation with Anton this evening). There are other features that are not really changes to the PARSE dialect, and so are out of scope for these proposals. That doesn't mean that they won't be implemented, just that they are a separate subject. That includes delimiter parsing (sorry, Petr), tracing (sorry, Henrik), REBOL language syntax (sorry, Graham), and port parsing (sorry, Steeve, Anton, Doc, Tomc, et al). If it makes you feel better, while discussing the subject with Anton here I figured out a way to do port parsing with the R3 port model (it wouldn't work with the R2 port model). I will bring these all up with Carl when it comes to that. I hope that this makes the situation and my position on the subject clearer. I'm sorry for any misunderstandings that arose during this process. | |
Note that I am quite familiar with collecting data from hierarchical and other structures and putting that data into hierarchical and other data structures. I have done this with PARSE, with DO dialect code, and with a combination of the two. I have found that PARSE is good for recognition, but DO dialect code is best for the construction. A mix of both is usually the best strategy. You can use the existing COLLECT and KEEP with PARSE quite well. PARSE is not a standalone dialect - it is meant to be integrated with other dialects, particularly the DO dialect that gets executed in the parens. | |
However, most of my contributions to REBOL.org were lost during one of their reorgs years ago and I have been mostly contributing in other ways lately. Like helping people out here and writing REBOL's mezzanine functions. I barely go to REBOL.org anymore except to search the code there for mezzanine usage so that I know what is safe to change. Outside of work that goes into REBOL community projects, most of my scripts have been either one-offs or under NDA lately. Sorry. | |
Sunanda 8-Nov-2008 [2938] | BrianH -- is it possible to incorporate the TRACE/DEBUG suggesion as part of the doc? Parse is so complex/deep/subtle that it needs some transparency. See my earlier message above, or here: http://www.rebol.org/aga-display-posts.r?post=r3wp210x2855 |
BrianH 8-Nov-2008 [2939x3] | I have been a member of the REBOL community, of varying activity, since 1999. If you have used REBOL in the 21st century you have probably used code I wrote. I understand the confusion - I was not very social for a while. |
Oh, that was your suggestion? I thought it was Henrik. It's on the list, and thanks for the link :) | |
Right now the Parse Proposals doc is for dialect enhancements. I am keeping a list of improvements out of that scope that will get worked on as well. Don't worry... | |
Sunanda 8-Nov-2008 [2942] | Thanks -- I'm sure I'm not the first to have had the idea. |
BrianH 8-Nov-2008 [2943x4] | You aren't, but it's still a good idea :) |
I'm glad that we are finally planning on PARSE improvements. PARSE has been the primary REBOL feature I've used for 8 years now. | |
That was a lot of writing - I must have gotten angry after all. | |
I forget sometimes that the REBOL community has been around long enough that many of the people from the early days aren't here anymore. I guess a lot of people don't remember me from the latter part of the REBOL 1 days and think I am a newbie. Sorry :( | |
Graham 8-Nov-2008 [2947] | Yep, I'm using code that you've written Brian :) Probably from years ago ! |
BrianH 8-Nov-2008 [2948x4] | I am sorry if it seemed like I was taking credit for various PARSE proposals. It is not anyone's fault that I have been using PARSE long enough that 7 or more years ago I came up with almost every one of those proposals, or their original inspirations. That's where the conversations that led to the REPs came from. There weren't as many REBOL users back before the Official Guide and REBOL for Dummies :) If other people who have had the same ideas since would like to add their names to the appropriate proposals I would be more than happy to help - consider them to be votes. I would be happier still if someone came up with a better way to do THROW or DO, because I am at a loss to figure out a way that isn't dumb :( |
I am embarrassed that the best, most obvious proposal is one that I completely spaced on. Congrats on REVERSE, Carl :) | |
It never occured to me or anyone else who was talking about enhancing PARSE in days of yore, not even Ladislav :( | |
Thanks, Graham :) | |
Graham 8-Nov-2008 [2952] | Pekr, Gabriele, Tomc, yourself and I are probably the longest Rebolers here these days |
BrianH 8-Nov-2008 [2953] | btw Sunanda, I can't remember who was the first to think of having trace support for PARSE, but it wasn't me :) |
Graham 8-Nov-2008 [2954] | Is attribution really important? |
BrianH 8-Nov-2008 [2955] | Steeve has indicated that it is. |
Graham 8-Nov-2008 [2956] | Is the driving force for fixing parse so that it can better parse data, or, to build better dialects, or both? |
BrianH 8-Nov-2008 [2957x3] | Strangely enough I wasn't talking about code I had posted that you might have used. In the early days before REBOL.org, I tended to post code to the mailing list. The code that you would have used would have been in REBOL itself - I used to give very detailed messages to feedback about mezzanine bugs, usually with rewrites. Many of those rewrites made it into REBOL, especially in the 2.5 version. Some natives too (to-local-file and to-rebol-file were based on REBOL code I wrote and posted). |
Right now the driving force is building better dialects - Carl needs it for the new GUI dialects. The data parsing improvements have just accumulated over the years and now seems like as good a time as any, especially because of the R3 compatibility break. | |
Some are needed because of Unicode. You can't effectively complement a charset anymore so NOT is needed. | |
Graham 8-Nov-2008 [2960x2] | ahh... so we can blame you for to-rebol-file problems?? :) |
http://members.core.com/~bhawley/rebol/to-rebol-file.r | |
BrianH 8-Nov-2008 [2962x2] | I can't shut down that website - my account was canceled more than 6 years ago and I can't access it. If you look elsewhere on the site you will find the only site on the internet with the Oberon Compiler for DOS - the developer disappeared without a trace. |
I've wanted to change the licensing on that script to BSD for years. It can do more than the native version - they simplified it. | |
Graham 8-Nov-2008 [2964] | Your CV is a bit out of date! |
BrianH 8-Nov-2008 [2965x3] | Can't edit the site :( |
Wow, that code is so primitive. | |
Except require.r - that is advanced even today. | |
Anton 8-Nov-2008 [2968] | I should just say that I really appreciate the enormous amount of energy that BrianH has put into this project (and generally). I can see there's a lot of work to manage all the proposals. |
Steeve 8-Nov-2008 [2969] | 2, 3 tips I know that Brian is great contributor but I think sometimes it tends to reject a bit too easily ideas of others. Why I am saying this, is that I am not always convinced by his arguments but he acts as if the issue was resolved in advance. (I may have a problem with that) About who is credited with what, I think that this is not important too, however it was a bit of supris seeing the name of Brian on most of the ideas, then as I said previously, this makes many years that these Improvements have been suggested by different people. Obviously this is not an important step, but Brian, you puting your name everywhere pretexting you collect ideas is a little ... how to say that ? pretentious. Personally, I am a large user of parsing. I think this is the most important function in Rebol. You can do practically everything with it. Design dialects, interfaces, and many others things. Parse can build programs by clearly showing the data structures your are dealing with. Thus our scripts win in readability. During all these years, I was very frustrated seeing some limitations. I thought, oh my God, if only we could do this simply, REBOL would be so powerful. My view is that parse should be extended (as far as possible) to gain in expressiveness. One thing I don't like with parse, is the cumbersome process to pass parameters to functions. I give an example. usually we do: [copy parm my-rule (my-func parm)] If parse knew recognize when to call a function we could write: [Myfunc my-rule] This would be much more compact and expressive. More, we could use return value of myfunc to guess if the parsing should continue or not. This development would discard most of proposals that were made because we could add many new commands very easily. (IF NOT ALL RETURN etc ...) |
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