Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!usenet.blueworldhosting.com!feeder01.blueworldhosting.com!border2.nntp.dca1.giganews.com!nntp.giganews.com!news.iecc.com!.POSTED!nerds-end From: George Neuner Newsgroups: comp.compilers Subject: Re: specifying semantics, was Formatting of Language LRMs Date: Sun, 29 Jun 2014 07:56:55 -0400 Organization: A noiseless patient Spider Lines: 50 Sender: news@iecc.com Approved: comp.compilers@iecc.com Message-ID: <14-06-030@comp.compilers> References: <14-06-010@comp.compilers> <14-06-023@comp.compilers> <14-06-025@comp.compilers> <14-06-027@comp.compilers> NNTP-Posting-Host: news.iecc.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Trace: miucha.iecc.com 1404055705 6795 2001:470:1f07:1126:0:676f:7373:6970 (29 Jun 2014 15:28:25 GMT) X-Complaints-To: abuse@iecc.com NNTP-Posting-Date: Sun, 29 Jun 2014 15:28:25 +0000 (UTC) Keywords: semantics Posted-Date: 29 Jun 2014 11:28:25 EDT X-submission-address: compilers@iecc.com X-moderator-address: compilers-request@iecc.com X-FAQ-and-archives: http://compilers.iecc.com Xref: csiph.com comp.compilers:1285 Hi Ivan, On Sat, 28 Jun 2014 12:25:18 -0700, Ivan Godard wrote: >Where would you place VWG on the operational/denotational/axiomatic >spectrum? Denotational. Technically any grammar formalism is a denotational description of the syntax of the accepted/generated language. But I think what you really may be asking is whether a vW-grammar also is a semantic description of the language it describes. The only place I have seen a 2 level grammar used was in the original Algol68 report. Despite the inclusion of semantically meaningful terms like "inseparable" and "strongly", etc., in actuality the vW grammar in the report was used only for syntax specification. Language semantics were not described *using* the formalism but rather were given by accompanying text and only were *referenced* by the formalism. [Quickly reviewing the reports I noticed that the revised report adopted a different (though equally dense) 2 level grammar "to make its study easier for the uninitiated reader". Honestly, I don't see how the "NEST" grammar was any improvement on the vW.] At the most basic, any grammar imparts some (very limited) semantics to the described language by constraining[*] the symbolic alphabet and the set of strings that are to be considered valid. However, the meaning of those strings is knowable only to an observer/manipulator at a level higher than the grammar that describes them. [*] Even though the set of valid strings may, in fact, be infinite, owing to constraints the set must be countably infinite and therefore (theoretically) enumerable. 8-) Of course, 2-level grammars like vW can be shown to be Turing Complete - so in theory one could describe Yet Another Grammar which, in turn, could be used to describe both the syntax and denotation semantics of Yet Another Language. I can imagine that the YAG is some sort of a declarative programming language in its own right and the YAL is a program "written" in YAG which is (or generates) the compiler for YAL. Ouch! I've just gotten a meta-circular headache! George