September Morn Update

Task/List-comprehensions/Python/list-comprehensions-8.py

@@ -0,0 +1,59 @@
+from functools import (reduce)
+from operator import (add)
+
+
+# pts :: Int -> [(Int, Int, Int)]
+def pts(n):
+    m = 1 + n
+    return [(x, y, z) for x in xrange(1, m)
+            for y in xrange(x, m)
+            for z in xrange(y, m) if x**2 + y**2 == z**2]
+
+
+# pts2 :: Int -> [(Int, Int, Int)]
+def pts2(n):
+    m = 1 + n
+    return bindList(
+        xrange(1, m)
+    )(lambda x: bindList(
+        xrange(x, m)
+    )(lambda y: bindList(
+        xrange(y, m)
+    )(lambda z: [(x, y, z)] if x**2 + y**2 == z**2 else [])))
+
+
+# pts3 :: Int -> [(Int, Int, Int)]
+def pts3(n):
+    m = 1 + n
+    return concatMap(
+        lambda x: concatMap(
+            lambda y: concatMap(
+                lambda z: [(x, y, z)] if x**2 + y**2 == z**2 else []
+            )(xrange(y, m))
+        )(xrange(x, m))
+    )(xrange(1, m))
+
+
+# GENERIC ---------------------------------------------------------
+
+# concatMap :: (a -> [b]) -> [a] -> [b]
+def concatMap(f):
+    return lambda xs: (
+        reduce(add, map(f, xs), [])
+    )
+
+
+# (flip concatMap)
+# bindList :: [a] -> (a -> [b])  -> [b]
+def bindList(xs):
+    return lambda f: (
+        reduce(add, map(f, xs), [])
+    )
+
+
+def main():
+    for f in [pts, pts2, pts3]:
+        print (f(20))
+
+
+main()