Data commit

Task/Range-extraction/Haskell/range-extraction-1.hs

@@ -0,0 +1,13 @@
+import Data.List (intercalate)
+
+extractRange :: [Int] -> String
+extractRange = intercalate "," . f
+  where f :: [Int] -> [String]
+        f (x1 : x2 : x3 : xs) | x1 + 1 == x2 && x2 + 1 == x3
+             = (show x1 ++ '-' : show xn) : f xs'
+          where (xn, xs') = g (x3 + 1) xs
+                g a (n : ns) | a == n    = g (a + 1) ns
+                             | otherwise = (a - 1, n : ns)
+                g a []                   = (a - 1, [])
+        f (x : xs)            = show x : f xs
+        f []                  = []

Task/Range-extraction/Haskell/range-extraction-2.hs

@@ -0,0 +1,2 @@
+> extractRange $ [0..2] ++ 4 : [6..8] ++ 11 : 12 : [14..25] ++ [27..33] ++ [35..39]
+"0-2,4,6-8,11,12,14-25,27-33,35-39"

Task/Range-extraction/Haskell/range-extraction-3.hs

@@ -0,0 +1,68 @@
+import Data.List (intercalate)
+import Data.Function (on)
+
+----------------------- RANGE FORMAT ---------------------
+rangeFormat :: [Int] -> String
+rangeFormat = intercalate "," . fmap rangeString . splitBy ((/=) . succ)
+
+rangeString xs
+  | 2 < length xs = x ++ '-' : last t
+  | otherwise = intercalate "," ps
+  where
+    ps@(x:t) = show <$> xs
+
+--------------------- GENERIC FUNCTION -------------------
+-- Split wherever a supplied predicate matches the
+-- relationship between two consecutive items.
+splitBy :: (a -> a -> Bool) -> [a] -> [[a]]
+splitBy _ [] = []
+splitBy _ [x] = [[x]]
+splitBy f xs@(_:t) = uncurry (:) $ foldr go ([], []) (zip xs t)
+  where
+    go (x, prev) (active, acc)
+      | f x prev = ([x], current : acc)
+      | otherwise = (x : current, acc)
+      where
+        current
+          | null active = [prev]
+          | otherwise = active
+
+--------------------------- TEST -------------------------
+main :: IO ()
+main =
+  print $
+  rangeFormat
+    [ 0
+    , 1
+    , 2
+    , 4
+    , 6
+    , 7
+    , 8
+    , 11
+    , 12
+    , 14
+    , 15
+    , 16
+    , 17
+    , 18
+    , 19
+    , 20
+    , 21
+    , 22
+    , 23
+    , 24
+    , 25
+    , 27
+    , 28
+    , 29
+    , 30
+    , 31
+    , 32
+    , 33
+    , 35
+    , 36
+    , 37
+    , 38
+    , 39
+    ]

Task/Range-extraction/Haskell/range-extraction-4.hs

@@ -0,0 +1,29 @@
+import Data.List (intercalate, groupBy, isPrefixOf)
+import Data.List.Split (chop)
+import Data.Bool (bool)
+
+rangeFormat :: [Int] -> String
+rangeFormat xs =
+  intercalate "," $
+  (head . ((bool <*> tail) <*> (> 1) . length)) <$>
+  groupBy isPrefixOf (rangeString <$> chop succSpan (zip xs (tail xs)))
+
+rangeString [] = ""
+rangeString xxs@(x:xs)
+  | null xs = show (snd x)
+  | otherwise = intercalate "-" (show <$> [fst x, snd (last xs)])
+
+succSpan [] = ([], [])
+succSpan (xxs@(x:xs))
+  | null ys = ([x], xs)
+  | otherwise = (ys, zs)
+  where
+    (ys, zs) = span (uncurry ((==) . succ)) xxs
+
+main :: IO ()
+main =
+  putStrLn $
+  rangeFormat [ 0, 1, 2, 4, 6, 7, 8, 11, 12, 14,
+      15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
+      25, 27, 28, 29, 30, 31, 32, 33, 35, 36,
+      37, 38, 39 ]