tasks a-s

Task/Roman-numerals-Encode/Mathematica/roman-numerals-encode-4.math

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+:- module roman.
+
+:- interface.
+
+:- import_module io.
+
+:- pred main(io::di, io::uo) is det.
+
+:- implementation.
+
+:- import_module char, int, list, string.
+
+main(!IO) :-
+    command_line_arguments(Args, !IO),
+    filter(is_all_digits, Args, CleanArgs),
+    foldl((pred(Arg::in, !.IO::di, !:IO::uo) is det :-
+               ( Roman = to_roman(Arg) ->
+                     format("%s => %s", [s(Arg), s(Roman)], !IO), nl(!IO)
+               ;     format("%s cannot be converted.", [s(Arg)], !IO), nl(!IO) )
+          ), CleanArgs, !IO).
+
+:- func to_roman(string::in) = (string::out) is semidet.
+to_roman(Number) = from_char_list(build_roman(reverse(to_char_list(Number)))).
+
+:- func build_roman(list(char)) = list(char).
+:- mode build_roman(in)         = out is semidet.
+build_roman([]) = [].
+build_roman([D|R]) = Roman :-
+    map(promote, build_roman(R), Interim),
+    Roman = Interim ++ digit_to_roman(D).
+
+:- func digit_to_roman(char) = list(char).
+:- mode digit_to_roman(in)   = out is semidet.
+digit_to_roman('0') = [].
+digit_to_roman('1') = ['I'].
+digit_to_roman('2') = ['I','I'].
+digit_to_roman('3') = ['I','I','I'].
+digit_to_roman('4') = ['I','V'].
+digit_to_roman('5') = ['V'].
+digit_to_roman('6') = ['V','I'].
+digit_to_roman('7') = ['V','I','I'].
+digit_to_roman('8') = ['V','I','I','I'].
+digit_to_roman('9') = ['I','X'].
+
+:- pred promote(char::in, char::out) is semidet.
+promote('I', 'X').
+promote('V', 'L').
+promote('X', 'C').
+promote('L', 'D').
+promote('C', 'M').
+
+:- end_module roman.