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| About finding the start symbol of a grammar ecosta.tmp@gmail.com (Eduardo Costa) (2021-05-21) |
| Re: About finding the start symbol of a grammar 563-365-8930@kylheku.com (Kaz Kylheku) (2021-05-21) |
| Re: About finding the start symbol of a grammar DrDiettrich1@netscape.net (Hans-Peter Diettrich) (2021-05-21) |
| Re: About finding the start symbol of a grammar anton@mips.complang.tuwien.ac.at (2021-05-21) |
| Re: About finding the start symbol of a grammar drikosev@gmail.com (Ev. Drikos) (2021-05-22) |
| Re: About finding the start symbol of a grammar gah4@u.washington.edu (gah4) (2021-05-22) |
| From: | "Ev. Drikos" <drikosev@gmail.com> |
| Newsgroups: | comp.compilers |
| Date: | Sat, 22 May 2021 06:52:17 +0300 |
| Organization: | Aioe.org NNTP Server |
| References: | 21-05-015 |
| Injection-Info: | gal.iecc.com; posting-host="news.iecc.com:2001:470:1f07:1126:0:676f:7373:6970"; logging-data="33346"; mail-complaints-to="abuse@iecc.com" |
| Keywords: | parse |
| Posted-Date: | 22 May 2021 13:23:54 EDT |
| Content-Language: | en-US |
On 21/05/2021 13:49, Eduardo Costa wrote:
> While there would exist grammars we could recursively check to find out which
> it's start symbol is (i.e.: it's the only rule that used the rest of them,
> where checking every other resulted in dangling rules that weren't even called
> in), there might be other grammars for which more than one rule yields full
> coverage (all of these obviously defining different languages) and so leading
> to ambiguity.
IMHO, it can be so simple as you describe here without important overhead.
Typically, a parser will reduce the start symbol and finish. All rules
that yield full coverage can be ie alternatives of a single root symbol:
RootSymbol -> R1 | R2 | ... | Rn
Ev. Drikos
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