SOURCE_FILE
  FN
    FN_KW "fn"
    WHITESPACE " "
    NAME
      IDENT "foo"
    PARAM_LIST
      L_PAREN "("
      PARAM
        IDENT_PAT
          NAME
            IDENT "a"
        COLON ":"
        WHITESPACE " "
        PATH_TYPE
          PATH
            PATH_SEGMENT
              NAME_REF
                IDENT "A"
      R_PAREN ")"
    WHITESPACE " "
    BLOCK_EXPR
      STMT_LIST
        L_CURLY "{"
        WHITESPACE "\n    "
        FIELD_EXPR
          PATH_EXPR
            PATH
              PATH_SEGMENT
                NAME_REF
                  IDENT "a"
          DOT "."
        WHITESPACE "\n"
        R_CURLY "}"
  WHITESPACE "\n"
error 21: expected field name or number