anchor.diff:  
   type_casting_operator : 'is' type | 'as' '?'? type ;
   
  -// GRAMMAR OF A PRIMARY EXPRESSION
  -
  -primary_expression : identifier generic_argument_clause?
  - | literal_expression
  - | self_expression
  - | superclass_expression
  - | closure_expression
  - | parenthesized_expression
  - | implicit_member_expression
  - | wildcard_expression
  - ;
  -
  -// GRAMMAR OF A LITERAL EXPRESSION
  -
  -literal_expression : literal
  - | array_literal | dictionary_literal
  - | '__FILE__' | '__LINE__' | '__COLUMN__' | '__FUNCTION__'  ;
  -array_literal : '[' array_literal_items? ']'  ;
  -array_literal_items : array_literal_item ','?  array_literal_item ',' array_literal_items  ;
  -array_literal_item : expression  ;
  -dictionary_literal : '[' dictionary_literal_items ']' | '[' ':' ']'  ;
  -dictionary_literal_items : dictionary_literal_item ','?  dictionary_literal_item ',' dictionary_literal_items  ;
  -dictionary_literal_item : expression ':' expression  ;
  -
  -// GRAMMAR OF A SELF EXPRESSION
  -
  -self_expression : 'self'
  - | 'self' '.' identifier
  - | 'self' '[' expression ']'
  - | 'self' '.' 'init'
  - ;
  -
  -// GRAMMAR OF A SUPERCLASS EXPRESSION
  -
  -superclass_expression : superclass_method_expression | superclass_subscript_expression  superclass_initializer_expression  ;
  -superclass_method_expression : 'super' '.' identifier  ;
  -superclass_subscript_expression : 'super' '[' expression ']'  ;
  -superclass_initializer_expression : 'super' '.' 'init'  ;
  -
  -// GRAMMAR OF A CLOSURE EXPRESSION
  -
  -closure_expression : '{' closure_signature? statements '}'  ;
  -closure_signature : parameter_clause function_result? 'in'
  - | identifier_list function_result? 'in'
  - | capture_list parameter_clause function_result? 'in'
  - | capture_list identifier_list function_result? 'in'
  - | capture_list 'in'
  - ;
  -capture_list : '[' capture_specifier expression ']'  ;
  -capture_specifier : 'weak' | 'unowned' | 'unowned(safe)' | 'unowned(unsafe)'  ;
  -
  -// GRAMMAR OF A IMPLICIT MEMBER EXPRESSION
  -
  -implicit_member_expression : '.' identifier  ;
  -
  -// GRAMMAR OF A PARENTHESIZED EXPRESSION
  -
  -parenthesized_expression : '('  expression_element_list? ')'  ;
  -expression_element_list : expression_element | expression_element ',' expression_element_list  ;
  -expression_element : expression | identifier ':' expression  ;
  -
  -// GRAMMAR OF A WILDCARD EXPRESSION
  -
  -wildcard_expression : '_'  ;
  -
   // GRAMMAR OF A POSTFIX EXPRESSION
   
  +/*
   postfix_expression : primary_expression
    | postfix_expression postfix_operator
    | function_call_expression
  
positive.code: 
  // GRAMMAR OF A TUPLE PATTERN
  
  tuple_pattern : ( tuple_pattern_element_list?)  ;
  tuple_pattern_element_list : tuple_pattern_element | tuple_pattern_element ',' tuple_pattern_element_list  ;
  tuple_pattern_element : pattern  ;
  
  // GRAMMAR OF AN ENUMERATION CASE PATTERN
  
  enum_case_pattern : type_identifier?. enum_case_name tuple_pattern? ;
  
  // GRAMMAR OF A TYPE CASTING PATTERN
  
  
negative.code: 
  // GRAMMAR OF A PATTERN
  
  pattern
   : wildcard_pattern type_annotation?
   | identifier_pattern type_annotation?
   | value_binding_pattern
   | tuple_pattern type_annotation?
   | enum_case_pattern
   | 'is' type
   | pattern 'as' type
   | expression_pattern
   ;
  
  