Data commit

Task/Palindrome-dates/Python/palindrome-dates-1.py

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+'''Palindrome dates'''
+
+from datetime import datetime
+from itertools import chain
+
+
+# palinDay :: Int -> [ISO Date]
+def palinDay(y):
+    '''A possibly empty list containing the palindromic
+       date for the given year, if such a date exists.
+    '''
+    s = str(y)
+    r = s[::-1]
+    iso = '-'.join([s, r[0:2], r[2:]])
+    try:
+        datetime.strptime(iso, '%Y-%m-%d')
+        return [iso]
+    except ValueError:
+        return []
+
+
+# --------------------------TEST---------------------------
+# main :: IO ()
+def main():
+    '''Count and samples of palindromic dates [2021..9999]
+    '''
+    palinDates = list(chain.from_iterable(
+        map(palinDay, range(2021, 10000))
+    ))
+    for x in [
+            'Count of palindromic dates [2021..9999]:',
+            len(palinDates),
+            '\nFirst 15:',
+            '\n'.join(palinDates[0:15]),
+            '\nLast 15:',
+            '\n'.join(palinDates[-15:])
+    ]:
+        print(x)
+
+
+# MAIN ---
+if __name__ == '__main__':
+    main()

Task/Palindrome-dates/Python/palindrome-dates-2.py

@@ -0,0 +1,128 @@
+'''Palindrome dates'''
+
+from functools import reduce
+from itertools import chain
+from datetime import date
+
+
+# palinDay :: Integer -> [ISO Date]
+def palinDay(y):
+    '''A possibly empty list containing the palindromic
+       date for the given year, if such a date exists.
+    '''
+    [m, d] = [undigits(pair) for pair in chunksOf(2)(
+        reversedDecimalDigits(y)
+    )]
+    return [] if (
+        1 > m or m > 12 or 31 < d
+    ) else validISODate((y, m, d))
+
+
+# --------------------------TEST---------------------------
+# main :: IO ()
+def main():
+    '''Count and samples of palindromic dates [2021..9999]
+    '''
+    palinDates = list(chain.from_iterable(
+        map(palinDay, range(2021, 10000))
+    ))
+    for x in [
+            'Count of palindromic dates [2021..9999]:',
+            len(palinDates),
+            '\nFirst 15:',
+            '\n'.join(palinDates[0:15]),
+            '\nLast 15:',
+            '\n'.join(palinDates[-15:])
+    ]:
+        print(x)
+
+
+# -------------------------GENERIC-------------------------
+
+# Just :: a -> Maybe a
+def Just(x):
+    '''Constructor for an inhabited Maybe (option type) value.
+       Wrapper containing the result of a computation.
+    '''
+    return {'type': 'Maybe', 'Nothing': False, 'Just': x}
+
+
+# Nothing :: Maybe a
+def Nothing():
+    '''Constructor for an empty Maybe (option type) value.
+       Empty wrapper returned where a computation is not possible.
+    '''
+    return {'type': 'Maybe', 'Nothing': True}
+
+
+# chunksOf :: Int -> [a] -> [[a]]
+def chunksOf(n):
+    '''A series of lists of length n, subdividing the
+       contents of xs. Where the length of xs is not evenly
+       divible, the final list will be shorter than n.
+    '''
+    return lambda xs: reduce(
+        lambda a, i: a + [xs[i:n + i]],
+        range(0, len(xs), n), []
+    ) if 0 < n else []
+
+
+# reversedDecimalDigits :: Int -> [Int]
+def reversedDecimalDigits(n):
+    '''A list of the decimal digits of n,
+       in reversed sequence.
+    '''
+    return unfoldr(
+        lambda x: Nothing() if (
+            0 == x
+        ) else Just(divmod(x, 10))
+    )(n)
+
+
+# unDigits :: [Int] -> Int
+def undigits(xs):
+    '''An integer derived from a list of decimal digits
+    '''
+    return reduce(lambda a, x: a * 10 + x, xs, 0)
+
+
+# unfoldr(lambda x: Just((x, x - 1)) if 0 != x else Nothing())(10)
+# -> [10, 9, 8, 7, 6, 5, 4, 3, 2, 1]
+# unfoldr :: (b -> Maybe (a, b)) -> b -> [a]
+def unfoldr(f):
+    '''Dual to reduce or foldr.
+       Where catamorphism reduces a list to a summary value,
+       the anamorphic unfoldr builds a list from a seed value.
+       As long as f returns Just(a, b), a is prepended to the list,
+       and the residual b is used as the argument for the next
+       application of f.
+       When f returns Nothing, the completed list is returned.
+    '''
+    def go(v):
+        xr = v, v
+        xs = []
+        while True:
+            mb = f(xr[0])
+            if mb.get('Nothing'):
+                return xs
+            else:
+                xr = mb.get('Just')
+                xs.append(xr[1])
+        return xs
+    return go
+
+
+# validISODate :: (Int, Int, Int) -> [Date]
+def validISODate(ymd):
+    '''A possibly empty list containing the
+       ISO8601 string for a date, if that date exists.
+    '''
+    try:
+        return [date(*ymd).isoformat()]
+    except ValueError:
+        return []
+
+
+# MAIN ---
+if __name__ == '__main__':
+    main()