[antlr-interest] Hi,what means "=>"?

[=?GB2312?B?0MLC8g==?=]

I'm learning the samples,in TinyC demo,there is

declaration
 : (variable) => variable
 | function
 ;

I found "=>" in the manual.
  {...}?
 semantic predicate
 (...)=>
 syntactic predicate
These 2 sentences are too short to understand.
Can someone tell me about that ~

thx.
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