September 2017 Update

Task/Binary-search/Haskell/binary-search-1.hs

@@ -1,9 +0,0 @@
-binarySearch :: Integral a => (a -> Ordering) -> (a, a) -> Maybe a
-binarySearch p (low,high)
-  | high < low = Nothing
-  | otherwise =
-      let mid = (low + high) `div` 2 in
-      case p mid of
-        LT -> binarySearch p (low, mid-1)
-        GT -> binarySearch p (mid+1, high)
-        EQ -> Just mid

Task/Binary-search/Haskell/binary-search-2.hs

@@ -1,5 +0,0 @@
-import Data.Array
-
-binarySearchArray :: (Ix i, Integral i, Ord e) => Array i e -> e -> Maybe i
-binarySearchArray a x = binarySearch p (bounds a) where
-  p m = x `compare` (a ! m)

Task/Binary-search/Haskell/binary-search.hs

@@ -0,0 +1,52 @@
+import Data.Array (Array, Ix, (!), listArray, bounds)
+
+-- BINARY SEARCH --------------------------------------------------------------
+bSearch
+  :: Integral a
+  => (a -> Ordering) -> (a, a) -> Maybe a
+bSearch p (low, high)
+  | high < low = Nothing
+  | otherwise =
+    let mid = (low + high) `div` 2
+    in case p mid of
+         LT -> bSearch p (low, mid - 1)
+         GT -> bSearch p (mid + 1, high)
+         EQ -> Just mid
+
+-- Application to an array:
+bSearchArray
+  :: (Ix i, Integral i, Ord e)
+  => Array i e -> e -> Maybe i
+bSearchArray a x = bSearch (compare x . (a !)) (bounds a)
+
+-- TEST -----------------------------------------------------------------------
+axs
+  :: (Num i, Ix i)
+  => Array i String
+axs =
+  listArray
+    (0, 11)
+    [ "alpha"
+    , "beta"
+    , "delta"
+    , "epsilon"
+    , "eta"
+    , "gamma"
+    , "iota"
+    , "kappa"
+    , "lambda"
+    , "mu"
+    , "theta"
+    , "zeta"
+    ]
+
+main :: IO ()
+main =
+  let e = "mu"
+      found = bSearchArray axs e
+  in putStrLn $
+     '\'' :
+     e ++
+     case found of
+       Nothing -> "' Not found"
+       Just x -> "' found at index " ++ show x