Re: Problems with alternative in X3

On Wed, 23 Mar 2016 15:05:52 +0000
Mikael Asplund <[email protected]> wrote:
> Hi!
> 
> I have an issue with alternatives that I don't understand why it's
> happening. I've simplified it even down to just x3::attr():s and I
> still get the problem.
> 
> Example here (code also supplied in attachment):
> 
> http://coliru.stacked-crooked.com/a/bdf4718cdeb2db4d
> 
> Why does the commented out version on line 57 work, and the active
> one on line 58-59 not work? It's an alternative of two exactly equal
> sequences, shouldn't that result in them joining to the attribute
> type as the single sequence?
> 
> Regards,
>    Mikael
> 

SpiritX3 does not collapse when alternative branches are identical.
Instead, X3 requires the attribute after the expect parser to be a
variant type [0]; only `variant<Foo>` is permitted as an attribute.
SpiritV2 would remove the variant type from the expected type if it
held only a single type element, allowing `Foo`, `optional<Foo>`, and
`variant<Foo>` in this situation. Joel, which is the preferred
behavior? I can work on a patch + tests if the SpiritV2 approach should
be taken.

Lee

[0] http://coliru.stacked-crooked.com/a/e92c2c33db69af38

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