SOURCE_FILE
  FN
    FN_KW "fn"
    WHITESPACE " "
    NAME
      IDENT "f"
    PARAM_LIST
      L_PAREN "("
      R_PAREN ")"
    WHITESPACE " "
    BLOCK_EXPR
      STMT_LIST
        L_CURLY "{"
        WHITESPACE "\n    "
        PAREN_EXPR
          L_PAREN "("
          BIN_EXPR
            TRY_EXPR
              ATTR
                POUND "#"
                L_BRACK "["
                META
                  PATH
                    PATH_SEGMENT
                      NAME_REF
                        IDENT "a"
                R_BRACK "]"
              WHITESPACE " "
              PATH_EXPR
                PATH
                  PATH_SEGMENT
                    NAME_REF
                      IDENT "lhs"
              QUESTION "?"
            WHITESPACE " "
            PLUS "+"
            WHITESPACE " "
            AWAIT_EXPR
              ATTR
                POUND "#"
                L_BRACK "["
                META
                  PATH
                    PATH_SEGMENT
                      NAME_REF
                        IDENT "b"
                R_BRACK "]"
              WHITESPACE " "
              PATH_EXPR
                PATH
                  PATH_SEGMENT
                    NAME_REF
                      IDENT "rhs"
              DOT "."
              AWAIT_KW "await"
          R_PAREN ")"
        WHITESPACE "\n"
        R_CURLY "}"
  WHITESPACE "\n"
