anchor.diff:          (function_definition |
               new_type_definition |
               global_const_definition |
  -            import_statement)
  +            import_statement |
  +            stmt)
       ;
   
   new_type_definition:
  
positive.code:  */
  grammar ExM;
  
  options {output=AST;}
  
  tokens {
      PLUS    = '+' ;
  
negative.code:     ;
  
  // only allow function calls as non-assignment statements
  expr_stmt: 
        e=function_call -> ^( EXPR_STMT $e )      
      | e=variable -> ^( EXPR_STMT $e )
      ;
  
  update_stmt: v=ID LT cmd=ID GT MUTATE expr SEMICOLON
  