Improved project structure.

haskell/e001.hs

@@ -0,0 +1,51 @@
+import Data.Function
+import Data.List
+import qualified Data.Set as S
+
+-- 1 - sum of numbers ...
+problem_1 :: Int
+problem_1 = sum . nub $ [3,6..999] ++ [5,10..999]
+problem_1' = sum $ union [3,6..999] [5,10..999]
+main = problem_1'
+
+-- bcs.h
+import Prelude hiding ((>>=), return)
+
+type Choice a = [a]
+
+choose :: [a] -> Choice a
+choose xs = xs
+
+pair456 :: Int -> Choice (Int, Int)
+pair456 x = choose [(x, 4), (x, 5), (x, 6)]
+
+join :: Choice (Choice a) -> Choice a
+join = concat
+
+-- join $ map pair456 [1,2,3] 
+-- [1, 2, 3] >>= pair456
+(>>=) :: Choice a -> (a -> Choice b) -> Choice b
+choices >>= f = join (map f choices)
+
+return :: a -> Choice a
+return x = [x]
+
+makePairs :: Choice (Int, Int)
+makePairs = 
+  choose [1, 2, 3] >>= (\x ->
+  choose [4, 5, 6] >>= (\y ->
+  return (x, y)))
+
+mzero :: Choice a
+mzero = choose []
+
+guard :: Bool -> Choice ()
+guard True  = return ()
+guard False = mzero
+
+makePairs' :: Choice (Int,Int)
+makePairs' = do
+  x <- choose [1,2,3]
+  y <- choose [4,5,6]
+  guard (x*y == 8)
+  return (x,y)