September Morn Update

Task/Binary-digits/Python/binary-digits-4.py

@@ -0,0 +1,90 @@
+'''Binary strings for integers'''
+
+
+# showBinary :: Int -> String
+def showBinary(n):
+    '''Binary string representation of an integer.'''
+    def binaryChar(n):
+        return '1' if n != 0 else '0'
+    return showIntAtBase(2)(binaryChar)(n)('')
+
+
+# TEST ----------------------------------------------------
+
+# main :: IO()
+def main():
+    '''Test'''
+
+    print('Mapping showBinary over integer list:')
+    print(unlines(map(
+        showBinary,
+        [5, 50, 9000]
+    )))
+
+    print(tabulated(
+        '\nUsing showBinary as a display function:'
+    )(str)(showBinary)(
+        lambda x: x
+    )([5, 50, 9000]))
+
+
+# GENERIC -------------------------------------------------
+
+# compose (<<<) :: (b -> c) -> (a -> b) -> a -> c
+def compose(g):
+    '''Right to left function composition.'''
+    return lambda f: lambda x: g(f(x))
+
+
+# enumFromTo :: (Int, Int) -> [Int]
+def enumFromTo(m):
+    '''Integer enumeration from m to n.'''
+    return lambda n: list(range(m, 1 + n))
+
+
+# showIntAtBase :: Int -> (Int -> String) -> Int -> String -> String
+def showIntAtBase(base):
+    '''String representing a non-negative integer
+       using the base specified by the first argument,
+       and the character representation specified by the second.
+       The final argument is a (possibly empty) string to which
+       the numeric string will be prepended.'''
+    def wrap(toChr, n, rs):
+        def go(nd, r):
+            n, d = nd
+            r_ = toChr(d) + r
+            return go(divmod(n, base), r_) if 0 != n else r_
+        return 'unsupported base' if 1 >= base else (
+            'negative number' if 0 > n else (
+                go(divmod(n, base), rs))
+        )
+    return lambda toChr: lambda n: lambda rs: (
+        wrap(toChr, n, rs)
+    )
+
+
+# tabulated :: String -> (a -> String) ->
+#                        (b -> String) ->
+#                        (a -> b) -> [a] -> String
+def tabulated(s):
+    '''Heading -> x display function -> fx display function ->
+                f -> value list -> tabular string.'''
+    def go(xShow, fxShow, f, xs):
+        w = max(map(compose(len)(xShow), xs))
+        return s + '\n' + '\n'.join(
+            xShow(x).rjust(w, ' ') + ' -> ' + fxShow(f(x)) for x in xs
+        )
+    return lambda xShow: lambda fxShow: lambda f: lambda xs: go(
+        xShow, fxShow, f, xs
+    )
+
+
+# unlines :: [String] -> String
+def unlines(xs):
+    '''A single string derived by the intercalation
+       of a list of strings with the newline character.'''
+    return '\n'.join(xs)
+
+
+if __name__ == '__main__':
+    main()