Re: Why do some versions of bison require {} here?

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
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[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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