anchor.diff:  primaryExpr
       : operand
       | conversion
  -    | primaryExpr ( selector
  +    | primaryExpr ( DOT IDENTIFIER
                     | index
                     | slice
                     | typeAssertion
  
positive.code:     ;
  
  parameters
      : '(' (parameterList ','?)? ')'
      ;
  
  parameterList
      : parameterDecl (',' parameterDecl)*
      ;
  
  parameterDecl
      : identifierList? '...'? type
  
negative.code:     : string
      ;
  
  /*topLevelDecl
      : declaration
      | functionDecl
      | methodDecl
      ;
  */
  
  declaration
      : constDecl
  