罗马到数字转换 erlang

-module(fromroman).

-compile(export_all).

fromroman(RomanChar) ->

 Pattern = "^(M{0,3})(CM|CD|D?C{0,3})(XC|XL|L?X{0,3})(IX|IV|V?I{0,3})$",

 {match, RomanList} = re:run(RomanChar, Pattern, [{capture, all_but_first, list}]),

 NewRomanList = lists:zip(RomanList, [1000, 100, 10, 1]),

 NumStr = lists:foldl(fun(X, Sum) -> Sum ++ X end, "", lists:map(fun mapNum/1, NewRomanList)),

 list_to_integer(NumStr).

mapNum({"", _Level}) -> "0";

mapNum({Char, Level}) ->

 SeqStr = "IVXLCDM",

 Dict = #{ 1    =>  #{$I => 1, $V => 5, $X => 10},

     10   =>  #{$X => 1, $L => 5, $C => 10},  

     100  =>  #{$C => 1, $D => 5, $M => 10},

     1000 =>  #{$M => 1}},

 CharDict = maps:get(Level, Dict),

 MaxChar = lists:last(lists:usort(fun(X, Y)->

          string:chr(SeqStr, X) =< string:chr(SeqStr, Y) end, Char)),

 {DelList, AddList} = lists:splitwith(fun(Elem) -> Elem =/= MaxChar end, Char),

 MapFun = fun(Chr) -> maps:get(Chr, CharDict) end,

 integer_to_list(lists:sum(lists:map(MapFun, AddList)) - lists:sum(lists:map(MapFun, DelList))).