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Groups > comp.compilers > #2144
| From | Kaz Kylheku <157-073-9834@kylheku.com> |
|---|---|
| Newsgroups | comp.compilers |
| Subject | Re: Why do some versions of bison require {} here? |
| Date | 2019-01-02 19:29 +0000 |
| Organization | Aioe.org NNTP Server |
| Message-ID | <19-01-002@comp.compilers> (permalink) |
| References | <19-01-001@comp.compilers> |
On 2019-01-01, Philipp Klaus Krause <pkk@spth.de> wrote:
> | addressmod
> {
> }
> ;
>
> for their yacc / bison to accept the rule.
> What is happening here? Why is the {} required? Why only on the last
> rule, while the first one is okay?
>
> Philipp
> [Adding the empty action forces bison to reduce the rule rather than just
> shifting and saving state for later. I couldn't guess why that would matter
> in this case. Are there precedence rules? With your change does the grammar compile
> cleanly or does it have conflicts? -John]
What, John? Shouldn't a missing action be equivalent to { $$ = $1 }?
Here, found it in Bison's manual, "3.4.6 Actions":
If you don’t specify an action for a rule, Bison supplies
a default: $$ = $1.
That should imply that there in fact is an action that requires a
reduction. Unless Bison handles this case specially without a reduce
somehow?
--
TXR Programming Lanuage: http://nongnu.org/txr
Music DIY Mailing List: http://www.kylheku.com/diy
ADA MP-1 Mailing List: http://www.kylheku.com/mp1
[Oops, you're quite right. It's been a decade since I revised
flex+bison and the brain cells are tired. Now I'm just baffled
unless there is some syntax error that the extra rule is somehow
fixing. -John]
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Why do some versions of bison require {} here? Philipp Klaus Krause <pkk@spth.de> - 2019-01-01 10:55 +0100
Re: Why do some versions of bison require {} here? Kaz Kylheku <157-073-9834@kylheku.com> - 2019-01-02 19:29 +0000
Re: Why do some versions of bison require {} here? Philipp Klaus Krause <pkk@spth.de> - 2019-01-03 09:15 +0100
Re: Why do some versions of bison require {} here? Kaz Kylheku <157-073-9834@kylheku.com> - 2019-01-04 03:02 +0000
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