September Morn Update

Task/Roman-numerals-Encode/Python/roman-numerals-encode-6.py

@@ -0,0 +1,64 @@
+'''Encoding Roman Numerals'''
+
+from functools import reduce
+from itertools import chain
+
+
+# romanFromInt ::  Int -> String
+def romanFromInt(n):
+    '''A string of Roman numerals encoding an integer.'''
+    def go(a, ms):
+        m, s = ms
+        q, r = divmod(a, m)
+        return (r, s * q)
+    return concat(snd(mapAccumL(go)(n)(
+        zip([1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1],
+            ['M', 'CM', 'D', 'CD', 'C', 'XC', 'L', 'XL', 'X', 'IX',
+             'V', 'IV', 'I'])
+    )))
+
+
+# MAIN -------------------------------------------------
+# main :: IO ()
+def main():
+    '''Test'''
+    print(
+        list(map(romanFromInt, [1666, 1990, 2008, 2016, 2018]))
+    )
+
+
+# GENERIC FUNCTIONS ---------------------------------------
+
+# concat :: [[a]] -> [a]
+# concat :: [String] -> String
+def concat(xxs):
+    '''The concatenation of all the elements in a list.'''
+    xs = list(chain.from_iterable(xxs))
+    unit = '' if isinstance(xs, str) else []
+    return unit if not xs else (
+        ''.join(xs) if isinstance(xs[0], str) else xs
+    )
+
+
+# mapAccumL :: (acc -> x -> (acc, y)) -> acc -> [x] -> (acc, [y])
+def mapAccumL(f):
+    '''A tuple of an accumulation and a list derived by a
+       combined map and fold,
+       with accumulation from left to right.'''
+    def go(a, x):
+        tpl = f(a[0], x)
+        return (tpl[0], a[1] + [tpl[1]])
+    return lambda acc: lambda xs: (
+        reduce(go, xs, (acc, []))
+    )
+
+
+# snd :: (a, b) -> b
+def snd(tpl):
+    '''Second component of a tuple.'''
+    return tpl[1]
+
+
+# MAIN ---
+if __name__ == '__main__':
+    main()