March 2014 update

Task/Roman-numerals-Decode/D/roman-numerals-decode-2.d

@@ -1,9 +1,8 @@
-import std.regex, std.algorithm, std.functional;
-
-alias sum = curry!(reduce!q{a + b}, 0);
+import std.regex, std.algorithm;
 
 immutable int[string] w2s;
-nothrow static this() {
+
+pure nothrow static this() {
     w2s = ["IX":  9, "C":  100, "D":  500, "CM": 900, "I":   1,
            "XC": 90, "M": 1000, "L":   50, "CD": 400, "XL": 40,
            "V":   5, "X":   10, "IV":   4];

Task/Roman-numerals-Decode/Mercury/roman-numerals-decode.mercury

@@ -0,0 +1,49 @@
+:- module test_roman.
+
+:- interface.
+
+:- import_module io.
+
+:- pred main(io::di, io::uo) is det.
+
+:- implementation.
+
+:- import_module char.
+:- import_module exception.
+:- import_module int.
+:- import_module list.
+:- import_module string.
+
+:- type conversion_error --->  not_a_roman_number.
+
+:- func build_int(list(char), int, int) = int.
+:- func from_roman(string) = int.
+:- pred roman_to_int(char::in, int::out) is semidet.
+
+from_roman(Roman) = Decimal :-
+  List = reverse(to_char_list(Roman)),
+  Decimal = build_int(List, 0, 0).
+
+build_int([], LastValue, Accumulator) = LastValue + Accumulator.
+build_int([Digit|Rest], LastValue, Accumulator) = Sum :-
+  ( roman_to_int(Digit, Value) ->
+      ( Value < LastValue ->
+          Sum = build_int(Rest, Value, Accumulator - LastValue)
+      ;   Sum = build_int(Rest, Value, Accumulator + LastValue) )
+  ;   throw(not_a_roman_number) ).
+
+roman_to_int('I', 1).
+roman_to_int('V', 5).
+roman_to_int('X', 10).
+roman_to_int('L', 50).
+roman_to_int('C', 100).
+roman_to_int('D', 500).
+roman_to_int('M', 1000).
+
+main(!IO) :-
+    command_line_arguments(Args, !IO),
+    foldl((pred(Arg::in, !.IO::di, !:IO::uo) is det :-
+              format("%s => %d\n", [s(Arg), i(from_roman(Arg))], !IO)),
+          Args, !IO).
+
+:- end_module test_roman.

Task/Roman-numerals-Decode/Rust/roman-numerals-decode.rust

@@ -0,0 +1,37 @@
+struct RomanNumeral {
+  symbol: &'static str,
+  value: uint
+}
+
+static NUMERALS: [RomanNumeral, ..13] = [
+  RomanNumeral {symbol: "M",  value: 1000},
+  RomanNumeral {symbol: "CM", value: 900},
+  RomanNumeral {symbol: "D",  value: 500},
+  RomanNumeral {symbol: "CD", value: 400},
+  RomanNumeral {symbol: "C",  value: 100},
+  RomanNumeral {symbol: "XC", value: 90},
+  RomanNumeral {symbol: "L",  value: 50},
+  RomanNumeral {symbol: "XL", value: 40},
+  RomanNumeral {symbol: "X",  value: 10},
+  RomanNumeral {symbol: "IX", value: 9},
+  RomanNumeral {symbol: "V",  value: 5},
+  RomanNumeral {symbol: "IV", value: 4},
+  RomanNumeral {symbol: "I",  value: 1}
+];
+
+fn to_hindu(roman: &str) -> uint {
+  for numeral in NUMERALS.iter() {
+    if roman.starts_with(numeral.symbol) {
+      return numeral.value + to_hindu(roman.slice_from(numeral.symbol.len()));
+    }
+  }
+
+  return 0;
+}
+
+fn main() {
+  let roms = ["MMXIV", "MCMXCIX", "XXV", "MDCLXVI", "MMMDCCCLXXXVIII"];
+  for r in roms.iter() {
+    println!("{:s} = {:u}", *r, to_hindu(*r));
+  }
+}