SOURCE_FILE
  FN
    FN_KW "fn"
    WHITESPACE " "
    NAME
      IDENT "r"
    PARAM_LIST
      L_PAREN "("
      R_PAREN ")"
    WHITESPACE " "
    BLOCK_EXPR
      STMT_LIST
        L_CURLY "{"
        WHITESPACE "\n    "
        LET_STMT
          LET_KW "let"
          WHITESPACE " "
          IDENT_PAT
            NAME
              IDENT "ok"
          WHITESPACE " "
          EQ "="
          WHITESPACE " "
          MACRO_EXPR
            MACRO_CALL
              PATH
                PATH_SEGMENT
                  NAME_REF
                    IDENT "format_args"
              BANG "!"
              TOKEN_TREE
                L_PAREN "("
                STRING "\"\""
                R_PAREN ")"
          WHITESPACE " "
          LET_ELSE
            ELSE_KW "else"
            WHITESPACE " "
            BLOCK_EXPR
              STMT_LIST
                L_CURLY "{"
                WHITESPACE " "
                EXPR_STMT
                  RETURN_EXPR
                    RETURN_KW "return"
                  SEMICOLON ";"
                WHITESPACE " "
                R_CURLY "}"
          SEMICOLON ";"
        WHITESPACE "\n\n    "
        LET_STMT
          LET_KW "let"
          WHITESPACE " "
          IDENT_PAT
            NAME
              IDENT "bad"
          WHITESPACE " "
          EQ "="
          WHITESPACE " "
          MACRO_EXPR
            MACRO_CALL
              PATH
                PATH_SEGMENT
                  NAME_REF
                    IDENT "format_args"
              BANG "!"
              WHITESPACE " "
              TOKEN_TREE
                L_CURLY "{"
                STRING "\"\""
                R_CURLY "}"
          WHITESPACE " "
          LET_ELSE
            ELSE_KW "else"
            WHITESPACE " "
            BLOCK_EXPR
              STMT_LIST
                L_CURLY "{"
                WHITESPACE " "
                EXPR_STMT
                  RETURN_EXPR
                    RETURN_KW "return"
                  SEMICOLON ";"
                WHITESPACE " "
                R_CURLY "}"
          SEMICOLON ";"
        WHITESPACE "\n"
        R_CURLY "}"
  WHITESPACE "\n"
error 89: right curly brace `}` before `else` in a `let...else` statement not allowed
