Language grammar opinions
"Clive D.W. Feather" <clive@demon.net> Mon, 08 January 2007 16:10 UTC
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Date: Mon, 08 Jan 2007 16:10:09 +0000
From: "Clive D.W. Feather" <clive@demon.net>
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Subject: Language grammar opinions
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Unlike my previous message, this is my opinions on the proposed language grammar. It's mostly based on the comments in the grammar. I prefer to list the possible declaration types in the grammar, so would prefer the commented-out version of "declaration". There's a parsability problem. Consider the sequence: alpha, bravo, charlie, delta, echo, foxtrot, golf, hotel, india, juliet, kilo, lima, mike, november, oscar, papa, quebec, romeo, sierra, tango, uniform, victor, whisky, x-ray, yankee: zulu Only after you see the next token (semicolon or comma or arrow) do you know if this is a declaration with an unknown type, or a transition. This produces a shift/reduce conflict in yacc or other such parser generators. To resolve it, I would suggest reversing the order of declarations to *begin* with the type: STATE : alpha, bravo, charlie ; I'd also make the various types be reserved words, so you can't have a state called "message" or an action called "state". In fact, looking further, I suggest that assignments are actually a form of declaration and can both be written the same way: Title = "My example (version 2)"; STATE = alpha, bravo, charlie; Initial = alpha; and be the same concept in the grammar. Using = will eliminate some parsing problems. Identifiers like foo----bar: I know this looks strange, and it's possible to write a syntax that forbids it: identifier = ALPHA *(["-"] 1*ALNUM) but I'm not convinced that it's worth it. Note that ABNF itself allows both double dashes and trailing dashes. However, I think we could usefully avoid allowing "x----->x---" to be valid. [Oops, omission in my last message: I defined ALNUM.] I see no benefit in restricting the characters in double-quoted names. At the very least, why allow comma and semicolon but not full stop and colon? Why not allow parentheses? I would simply define it as: dquote-chars = SP / %x21 / %x23-7E ; Space and all printable characters except double quote -- Clive D.W. Feather | Work: <clive@demon.net> | Tel: +44 20 8495 6138 Internet Expert | Home: <clive@davros.org> | Fax: +44 870 051 9937 Demon Internet | WWW: http://www.davros.org | Mobile: +44 7973 377646 THUS plc | | _______________________________________________ Cosmogol mailing list Cosmogol@ietf.org https://www1.ietf.org/mailman/listinfo/cosmogol
- Language grammar opinions Clive D.W. Feather
- Re: Language grammar opinions Stephane Bortzmeyer
- Re: Language grammar opinions Clive D.W. Feather