implemented nth

src/Mtlstats/Util.hs

@@ -0,0 +1,29 @@
+{- |
+
+mtlstats
+Copyright (C) 2019 Rhéal Lamothe
+<rheal.lamothe@gmail.com>
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or (at
+your option) any later version.
+
+This program is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+-}
+
+module Mtlstats.Util (nth) where
+
+nth :: Int -> [a] -> Maybe a
+nth _ [] = Nothing
+nth n (x:xs)
+  | n == 0    = Just x
+  | n < 0     = Nothing
+  | otherwise = nth (pred n) xs

test/Spec.hs

@@ -26,6 +26,7 @@ import qualified FormatSpec as Format
 import qualified HandlersSpec as Handlers
 import qualified ReportSpec as Report
 import qualified TypesSpec as Types
+import qualified UtilSpec as Util
 
 main :: IO ()
 main = hspec $ do
@@ -34,3 +35,4 @@ main = hspec $ do
   Format.spec
   Handlers.spec
   Report.spec
+  Util.spec

test/UtilSpec.hs

@@ -0,0 +1,44 @@
+{-
+
+mtlstats
+Copyright (C) 2019 Rhéal Lamothe
+<rheal.lamothe@gmail.com>
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or (at
+your option) any later version.
+
+This program is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+-}
+
+module UtilSpec (spec) where
+
+import Test.Hspec (Spec, context, describe, it, shouldBe)
+
+import Mtlstats.Util
+
+spec :: Spec
+spec = describe "Mtlstats.Util"
+  nthSpec
+
+nthSpec :: Spec
+nthSpec = describe "nth" $ mapM_
+  (\(n, expected) -> context (show n) $
+    it ("should be " ++ show expected) $ let
+      xs = ["foo", "bar", "baz"]
+      in nth n xs `shouldBe` expected)
+  --  index, expected
+  [ ( 0,     Just "foo" )
+  , ( 1,     Just "bar" )
+  , ( 2,     Just "baz" )
+  , ( 3,     Nothing    )
+  , ( -1,    Nothing    )
+  ]