Re: lr.type option proposes lr(0) but says option is invalid.

[Akim Demaille]

Hi Simon,

> Le 28 févr. 2022 à 20:28, Simon Scatton <simon.scatton@outlook.fr> a écrit :
> 
> Hello,
> 
> I've been experiencing with bison's lr.type option yesterday and I found
> a strange thing.
> 
> When changing the lr.type option in my bison file I made a typo and I
> encountered this error message :
> 
> test.yy:1.1-21: error: invalid value for %define variable ‘lr.type’: ‘lalrr’
>    1 | %define lr.type ielrr
>      | ^~~~~~~~~~~~~~~~~~~~~
> test.yy:1.1-21: note: accepted value: ‘lr(0)’
> test.yy:1.1-21: note: accepted value: ‘lalr’
> test.yy:1.1-21: note: accepted value: ‘ielr’
> test.yy:1.1-21: note: accepted value: ‘canonical-lr’
> 
> 
> Then I saw that there was a mention of lr(0) as a valid value for this
> field and when trying to use it I got this error message :
> 
> test.yy:1.19: error: invalid character: ‘(’
>    1 | %define lr.type lr(0)
>      |                   ^
> test.yy:1.21: error: invalid character: ‘)’
>    1 | %define lr.type lr(0)
>      |                     ^
> test.yy:7.3-8.0: error: unexpected epilogue
>    7 | %%
>      |   ^
> test.yy:1.1-18: error: invalid value for %define variable ‘lr.type’: ‘lr’
>    1 | %define lr.type lr(0)
>      | ^~~~~~~~~~~~~~~~~~
> test.yy:1.1-18: note: accepted value: ‘lr(0)’
> test.yy:1.1-18: note: accepted value: ‘lalr’
> test.yy:1.1-18: note: accepted value: ‘ielr’
> test.yy:1.1-18: note: accepted value: ‘canonical-lr’
> 
> I am doing something wrong here to define that option ?

While I was conducting significant changes in the generation of the LR(0) 
automaton, I was annoyed by the fact that the LR(0) automaton is quite "hidden" 
and hard to get.  I needed it to debug.

So I have added the value lr(0) to the option, but did not document it on 
purpose: it stops the automaton generation at the LR(0) stage, but there is no 
support for this in the skeletons.  And the routines we use to parse option 
arguments are too honest: they do show all the possible values.

In other words, you found something which is intended to stay hidden, as a 
helping tool for Bison developers, but not something meant for Bison users.

Cheers!