anchor.diff:      : 'func' function
       ;
   
  -primaryExpr
  -    : operand
  -    | conversion
  -    | primaryExpr selector
  -    | primaryExpr index
  -    | primaryExpr slice
  -    | primaryExpr typeAssertion
  -    | primaryExpr arguments
  -    ;
  -
   selector
       : '.' IDENTIFIER
       ;
  
positive.code:     ;
  
  exprCaseClause
      : exprSwitchCase ':' statementList
      ;
  
  exprSwitchCase
      : 'case' expressionList | 'default'
      ;
  
  typeSwitchStmt
  
negative.code:     ;
  
  typeCaseClause
      : typeSwitchCase ':' statementList?
      ;
  
  typeSwitchCase
      : 'case' typeList
      | 'default'
      ;
  
  typeList
  