September Morn Update

Task/Dot-product/Python/dot-product-2.py

@@ -0,0 +1,91 @@
+'''Dot product'''
+
+from operator import (mul)
+
+
+# dotProduct :: Num a => [a] -> [a] -> Either String a
+def dotProduct(xs):
+    '''Either the dot product of xs and ys,
+       or a string reporting unmatched vector sizes.
+    '''
+    return lambda ys: Left('vector sizes differ') if (
+        len(xs) != len(ys)
+    ) else Right(sum(map(mul, xs, ys)))
+
+
+# TEST ----------------------------------------------------
+# main :: IO ()
+def main():
+    '''Dot product of other vectors with [1, 3, -5]'''
+
+    print(
+        fTable(main.__doc__ + ':\n')(str)(str)(
+            compose(
+                either(append('Undefined :: '))(str)
+            )(dotProduct([1, 3, -5]))
+        )([[4, -2, -1, 8], [4, -2], [4, 2, -1], [4, -2, -1]])
+    )
+
+
+# GENERIC -------------------------------------------------
+
+# Left :: a -> Either a b
+def Left(x):
+    '''Constructor for an empty Either (option type) value
+       with an associated string.
+    '''
+    return {'type': 'Either', 'Right': None, 'Left': x}
+
+
+# Right :: b -> Either a b
+def Right(x):
+    '''Constructor for a populated Either (option type) value'''
+    return {'type': 'Either', 'Left': None, 'Right': x}
+
+
+# append (++) :: [a] -> [a] -> [a]
+# append (++) :: String -> String -> String
+def append(xs):
+    '''Two lists or strings combined into one.'''
+    return lambda ys: xs + ys
+
+
+# compose (<<<) :: (b -> c) -> (a -> b) -> a -> c
+def compose(g):
+    '''Right to left function composition.'''
+    return lambda f: lambda x: g(f(x))
+
+
+# either :: (a -> c) -> (b -> c) -> Either a b -> c
+def either(fl):
+    '''The application of fl to e if e is a Left value,
+       or the application of fr to e if e is a Right value.
+    '''
+    return lambda fr: lambda e: fl(e['Left']) if (
+        None is e['Right']
+    ) else fr(e['Right'])
+
+
+# FORMATTING ----------------------------------------------
+
+# fTable :: String -> (a -> String) ->
+#                     (b -> String) -> (a -> b) -> [a] -> String
+def fTable(s):
+    '''Heading -> x display function -> fx display function ->
+                     f -> xs -> tabular string.
+    '''
+    def go(xShow, fxShow, f, xs):
+        ys = [xShow(x) for x in xs]
+        w = max(map(len, ys))
+        return s + '\n' + '\n'.join(map(
+            lambda x, y: y.rjust(w, ' ') + ' -> ' + fxShow(f(x)),
+            xs, ys
+        ))
+    return lambda xShow: lambda fxShow: lambda f: lambda xs: go(
+        xShow, fxShow, f, xs
+    )
+
+
+# MAIN ---
+if __name__ == '__main__':
+    main()