SOURCE_FILE
  FN
    FN_KW "fn"
    WHITESPACE " "
    NAME
      IDENT "o"
    PARAM_LIST
      L_PAREN "("
      R_PAREN ")"
    WHITESPACE " "
    RET_TYPE
      THIN_ARROW "->"
      WHITESPACE " "
      PATH_TYPE
        PATH
          PATH_SEGMENT
            NAME_REF
              IDENT "Result"
            GENERIC_ARG_LIST
              L_ANGLE "<"
              TYPE_ARG
                TUPLE_TYPE
                  L_PAREN "("
                  R_PAREN ")"
              COMMA ","
              WHITESPACE " "
              TYPE_ARG
                TUPLE_TYPE
                  L_PAREN "("
                  R_PAREN ")"
              R_ANGLE ">"
    WHITESPACE " "
    BLOCK_EXPR
      STMT_LIST
        L_CURLY "{"
        WHITESPACE "\n    "
        LET_STMT
          LET_KW "let"
          WHITESPACE " "
          IDENT_PAT
            NAME
              IDENT "foo"
          WHITESPACE " "
          EQ "="
          WHITESPACE " "
          YEET_EXPR
            DO_KW "do"
            WHITESPACE " "
            YEET_KW "yeet"
            WHITESPACE " "
            BLOCK_EXPR
              STMT_LIST
                L_CURLY "{"
                WHITESPACE "\n        "
                TUPLE_EXPR
                  L_PAREN "("
                  R_PAREN ")"
                WHITESPACE "\n    "
                R_CURLY "}"
          WHITESPACE " "
          LET_ELSE
            ELSE_KW "else"
            WHITESPACE " "
            BLOCK_EXPR
              STMT_LIST
                L_CURLY "{"
                WHITESPACE "\n        "
                EXPR_STMT
                  RETURN_EXPR
                    RETURN_KW "return"
                    WHITESPACE " "
                    CALL_EXPR
                      PATH_EXPR
                        PATH
                          PATH_SEGMENT
                            NAME_REF
                              IDENT "Ok"
                      ARG_LIST
                        L_PAREN "("
                        TUPLE_EXPR
                          L_PAREN "("
                          R_PAREN ")"
                        R_PAREN ")"
                  SEMICOLON ";"
                WHITESPACE "\n    "
                R_CURLY "}"
          SEMICOLON ";"
        WHITESPACE "\n"
        R_CURLY "}"
error 67: right curly brace `}` before `else` in a `let...else` statement not allowed
