Self-interest December 1998

self-interest@lists.selflanguage.org

4 participants
5 discussions

Announcing mySelf
by Stefan Matthias Aust 17 Feb '99

17 Feb '99

Hi! I've set up a web page for my first version of ``mySelf´´, my Self parser and simulator written in Smalltalk! If you like, check out http://freeweb.digiweb.com/computers/sma/ MySelf works both for VisualWorks Smalltalk and Squeak, however the Squeak port is really crude. As Squeak's syntax unfortunately doesn't conform with the "standard", I had to work around some problems, mainly the fact that "_" isn't a valid character in message names. Therefore, I recommend VisualWorks NC, which is also _much_ faster. Happy New Year! bye -- Stefan Matthias Aust // Are you ready to discover the twilight zone? ------------------------------------------------------------------------ eGroup home: http://www.eGroups.com/list/self-interest Free Web-based e-mail groups by eGroups.com

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Re: Grammar questions
by Stefan Matthias Aust 29 Dec '98

29 Dec '98

Dru Nelson wrote: >[Using VW Smalltalk] >Is this from T Gen or something else? Sounds neat. It's something else. I wrote scanner and parser from scratch without any generator program. No big deal for a grammar as small as for Self. >[Status of completition] >Yeah, I finished my lexer and it is time for the parser and code gen. >I don't really know how I will deal with some of those issues as well. >I'll tell you what, though, Smalltalk is a lot better to debug than >C. I sometimes get those nice gdb stack traces with the '??' as the name >for each function. :-) No comment :-) BTW, in the meantime I've nearly finished my parser and I can simulate most expressions. Because of the way I wrote the simulator, I cannot evaluate non-local-returns but otherwise, things work as expected. [snip] >Emulating Self with Smalltalk. I'm sure the Self guys will get a kick out >of that. Then you could run their Smalltalk emulation system under it. Probably :-) bye -- Stefan Matthias Aust // Are you ready to discover the twilight zone? ------------------------------------------------------------------------ eGroup home: http://www.eGroups.com/list/self-interest Free Web-based e-mail groups by eGroups.com

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Re: Grammar questions
by Stefan Matthias Aust 29 Dec '98

29 Dec '98

Dru, > I'm working on a parser too. So far, I've only implemented the >lexer portion. Your recent email on that shows that you have >discovered how to handle that. Perhaps I should tell you a little bit more about my program. I used VisualWorks smalltalk to implement the parser. A "SelfScanner" class implements the scanner (lexer) while a call called "SelfParser" does all the dirty work. The scanner provides token/value pairs which are used by the parser. With the exception of number tokens, all values are strings (or symbols, a special kind of constant String in Smalltalk). The parser maintains a token-push-back-stack which is needed for looking ahead in the token stream. I think the scanner is finished. The parser still needs work. I can parse most SELF expression already, but there's no real code generator yet. And of course, I don't know how to deal with expressions and parenthesis! I actually wrote that parser just out of curiosity. I wanted to study the original morphic code and wanted to get rid of all that superfluous information the original SELF source files are bloaded with. I thought perhaps I could write a small program to extract method definitions from these files. I incrementally extended this to a whole parser :-) Now, there's the intriguing idea to add a VM simulator to the system. I already create "SelfObject" instances for each method. Each contains a number of slots (one of SelfMutableDataSlot, SelfImmutableDataSlot, SelfAssignerSlot, SelfArgumentSlot and SelfMethodSlot) and a list of SelfExpression objects, which eventually will hold a parse tree of message send (and resend) operations. >As for the longest whitespace, personally that will >work, but I think that any of the '=-' or ('=' operator) should >be illegal. Well, I just try to implement the grammar. I don't reason about it :-) But (allow me one thought) if you make '=' an illegal operator, you need another operator for testing equality. Because '==' is already used to test identity, you cannot use this or you need to change the language even more. I'm not sure whether this would be a good idea. >C did this for the same reasons. '=- 1' vs '= -1' is >hard to read, the standard '-=' is much easier to read. As for many other things (perhaps too many) in SELF, this should be considered as a convention but not a rule expressed in the grammar. Otherwise I'd agree withh you. >Thanks for posting your questions (and answers). The info has >saved me _a_lot_ of time. You're welcome. bye -- Stefan Matthias Aust // Are you ready to discover the twilight zone? ------------------------------------------------------------------------ E-group home: http://www.eGroups.com/list/self-interest Free Web-based e-mail groups by eGroups.com

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Grammar questions
by Stefan Matthias Aust 22 Dec '98

22 Dec '98

Hi! I was trying to understand the Self grammar to implement a Self parser. I failed. Now I've a couple of questions regarding the ambiguities of the grammar. I'm working with the grammar shown in appendix 2.C of the Self 4.0 language reference. Currently, I've two problems: a) How can I distinguish a simple expression enclosed in parenthesis from an object definition - and b) how to detect the end of a slot list? I expanded the BNF rules to deal with message precedence as follows: expression = keyword-message keyword-message = binary-message {keyword-send} | resend... keyword-send = small-keyword keyword-message {cap-keyword keyword-message} binary-message = unary-message {binary-send} | resend... binary-send = operator unary-message unary-message = primary {unary-send} | resend... unary-send = identifier primary = [receiver] receiver = identifier | constant now, to allow expressions in parentheses, we need to add a rule receiver = "(" expression ")" however, now there's no chance to distinguish this from the regular-object definition, which is one alternative of constant, because "( 1 + 2 )" could also be a valid method object. Did I miss something here? The second problem is with operators. Appendix 2.B says about operators: op-char = ... '-' | '^' | '|' | ... operator = op-char {op-char} which especially means that ^ and | are valid operators and furthermore, that for example '=-1' is ambigious. Let's ignore _that_ problem for now. My trouble are ^ and | as operators. Currently, my parser will fail on (| a = 1 |) because it thinks that there's a slot "a" to which a binary expression is assigned of which the second part is missing. It doesn't detect the end of the slot list. My parser also fails on this, which might be a legal Self expression according to the grammar: (| | x = ( ... ) |) If "|" is a valid operator, it must be possible to use it in a binary-slot definition. Here's another problem with '^': ^12 can be parsed both as "self ^ 12" and "return 12". My solution would be to bann ^ and | as valid operators, but what does the Self spec say, what does the offical Self parser do? I need help. Thanks in advance, bye -- Stefan Matthias Aust // Are you ready to discover the twilight zone? ------------------------------------------------------------------------ E-group home: http://www.eGroups.com/list/self-interest Free Web-based e-mail groups by eGroups.com

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Quick question on Self Grammar
by Dru Nelson 11 Dec '98

11 Dec '98

I was reading the self grammar. Am I right in assuming that... doIt. or a: setSlot: 'x' With: doIt. works, by having the receiver of the unary message doIt (which is probably a slot), is parsed as a null token for each of these expressions. Which would imply the default 'self' :-) as the receiver? Just a quick check, ------------------------------------------------------------------------ Free Web-based e-mail groups -- http://www.eGroups.com

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Self-interest December 1998