[antlr-interest] semantics of the => operator

[Michael Bedward]

Hello Christian,

The => operator indicates a 'syntatic predictate'. It's a device for
selecting between two, otherwise ambiguous alternatives.

There is a terse definition here: https://wincent.com/wiki/ANTLR_predicates
and a slightly friendlier one here:
http://www.antlr.org/wiki/display/ANTLR3/How+to+remove+global+backtracking+from+your+grammar

I'd also recommend you get the ANTLR books.

Michael


On 25 November 2011 13:44, Christian <chwchw at gmx.de> wrote:
> Hi community,
>
> I stumble across the => operator and the following rule:
>
> arule
>  : (identifier generic_argument_list) => identifier generic_argument_list
>  | identifier
>  ;
>
> Why is this rule not equivalent to the following one?
>
> brule
>  : identifier generic_argument_list?
>  ;
>
> I admit that I do not find the operator on the antlr site, thus I do not
> read any documentation about the semantics of =>.
>
> Please, can someone tell me?
>
> Thanks,
> Christian
>
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