September 2017 Update

Task/Roman-numerals-Decode/JavaScript/roman-numerals-decode-1.js

@@ -1,19 +1,18 @@
 var Roman = {
-  Values: [['M', 1000], ['CM', 900], ['D',  500], ['CD', 400],
-           ['C',  100], ['XC',  90], ['L',  50],  ['XL',  40],
-           ['X',   10], ['IX',   9], ['V',   5],  ['IV',   4],
-           ['I',    1]],
-
+  Values: [['CM', 900],  ['CD', 400], ['XC',  90], ['XL',  40], ['IV', 4],
+           ['IX',   9], ['V',   5], ['X',   10], ['L',  50],
+           ['C',  100], ['M', 1000], ['I',    1], ['D',  500]],
+  UnmappedStr : 'Q',
   parse: function(str) {
     var result = 0
     for (var i=0; i<Roman.Values.length; ++i) {
       var pair = Roman.Values[i]
       var key = pair[0]
       var value = pair[1]
-      var regex = RegExp('^' + key)
+      var regex = RegExp(key)
       while (str.match(regex)) {
         result += value
-        str = str.replace(regex, '')
+        str = str.replace(regex, Roman.UnmappedStr)
       }
     }
     return result

Task/Roman-numerals-Decode/JavaScript/roman-numerals-decode-6.js

@@ -0,0 +1,35 @@
+(() => {
+    // romanValue :: String -> Int
+    const romanValue = s =>
+        s.length ? (() => {
+            const parse = [].concat(
+                ...glyphs.map(g => 0 === s.indexOf(g) ? (
+                    [dctTrans[g], s.substr(g.length)]
+                ) : [])
+            );
+            return parse[0] + romanValue(parse[1]);
+        })() : 0;
+
+    // dctTrans :: {romanKey: Integer}
+    const dctTrans = {
+        M: 1E3,
+        CM: 900,
+        D: 500,
+        CD: 400,
+        C: 100,
+        XC: 90,
+        L: 50,
+        XL: 40,
+        X: 10,
+        IX: 9,
+        V: 5,
+        IV: 4,
+        I: 1
+    };
+
+    // glyphs :: [romanKey]
+    const glyphs = Object.keys(dctTrans);
+
+    // TEST -------------------------------------------------------------------
+    return ["MCMXC", "MDCLXVI", "MMVIII", "MMMM"].map(romanValue);
+})();

Task/Roman-numerals-Decode/JavaScript/roman-numerals-decode-7.js

@@ -0,0 +1 @@
+[1990,1666,2008,4000]

Task/Roman-numerals-Decode/JavaScript/roman-numerals-decode-8.js

@@ -0,0 +1,52 @@
+(() => {
+
+    // Folding from right to left,
+    // lower leftward characters are subtracted,
+    // others are added.
+
+    // fromRoman :: String -> Int
+    const fromRoman = s =>
+        snd(foldr(
+            ([r, n], l) => [l, l >= r ? n + l : n - l], [0, 0],
+            map(charVal, stringChars(s))
+        ));
+
+    // charVal :: Char -> Maybe Int
+    const charVal = k => {
+        const v = {
+            I: 1,
+            V: 5,
+            X: 10,
+            L: 50,
+            C: 100,
+            D: 500,
+            M: 1000
+        }[k];
+        return v !== undefined ? v : 0;
+    };
+
+    // GENERIC FUNCTIONS ------------------------------------------------------
+
+    // foldr (a -> b -> b) -> b -> [a] -> b
+    const foldr = (f, a, xs) => xs.reduceRight(f, a);
+
+    // map :: (a -> b) -> [a] -> [b]
+    const map = (f, xs) => xs.map(f);
+
+    // snd :: (a, b) -> b
+    const snd = tpl => Array.isArray(tpl) ? tpl[1] : undefined;
+
+    // stringChars :: String -> [Char]
+    const stringChars = s => s.split('');
+
+    // show :: a -> String
+    const show = (...x) =>
+        JSON.stringify.apply(
+            null, x.length > 1 ? [x[1], null, x[0]] : x
+        );
+
+    // TEST -------------------------------------------------------------------
+    return show(
+        map(fromRoman, ["MDCLXVI", "MCMXC", "MMVIII", "MMXVI", "MMXVII"])
+    );
+})();