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    "
        LET_STMT
          LET_KW "let"
          WHITESPACE " "
          WILDCARD_PAT
            UNDERSCORE "_"
          WHITESPACE " "
          EQ "="
          WHITESPACE " "
          MATCH_EXPR
            MATCH_KW "match"
            WHITESPACE " "
            CALL_EXPR
              PATH_EXPR
                PATH
                  PATH_SEGMENT
                    NAME_REF
                      IDENT "Some"
              ARG_LIST
                L_PAREN "("
                LITERAL
                  INT_NUMBER "1"
                R_PAREN ")"
            WHITESPACE " "
            MATCH_ARM_LIST
              L_CURLY "{"
              WHITESPACE "\n        "
              MATCH_ARM
                TUPLE_STRUCT_PAT
                  PATH
                    PATH_SEGMENT
                      NAME_REF
                        IDENT "Some"
                  L_PAREN "("
                  WILDCARD_PAT
                    UNDERSCORE "_"
                  R_PAREN ")"
                WHITESPACE " "
                FAT_ARROW "=>"
                WHITESPACE " "
                LITERAL
                  INT_NUMBER "1"
                COMMA ","
              WHITESPACE "\n        "
              MATCH_ARM
                IDENT_PAT
                  NAME
                    IDENT "None"
                WHITESPACE " "
                FAT_ARROW "=>"
                WHITESPACE " "
                LITERAL
                  INT_NUMBER "2"
                COMMA ","
              WHITESPACE "\n    "
              R_CURLY "}"
          WHITESPACE " "
          LET_ELSE
            ELSE_KW "else"
            WHITESPACE " "
            BLOCK_EXPR
              STMT_LIST
                L_CURLY "{"
                WHITESPACE "\n        "
                RETURN_EXPR
                  RETURN_KW "return"
                WHITESPACE "\n    "
                R_CURLY "}"
          SEMICOLON ";"
        WHITESPACE "\n"
        R_CURLY "}"
error 83: right curly brace `}` before `else` in a `let...else` statement not allowed
