implemented getRung

src/Abacus.hs

@@ -24,7 +24,15 @@ License along with this program.  If not, see
 
 -}
 
-module Abacus (Abacus, newAbacus, getNumBeads, getNumRungs) where
+module Abacus (
+  Abacus,
+  newAbacus,
+  getNumBeads,
+  getNumRungs,
+  getRung,
+  ) where
+
+import Data.List (find)
 
 import Abacus.Internal
 
@@ -48,4 +56,16 @@ getNumBeads = abacusNumBeads
 getNumRungs :: Abacus -> Int
 getNumRungs = length . abacusRungs
 
+-- | Returns the number of beads slid across a given rung
+getRung
+  :: Int
+  -- ^ The rung number
+  -> Abacus
+  -- ^ Abacus being checked
+  -> Maybe Int
+  -- ^ The number of beads slid across (if the rung exists)
+getRung r a = snd <$> find
+  (\(n, _) -> n == r)
+  (zip [0..] $ abacusRungs a)
+
 --jl

test/AbacusSpec.hs

@@ -32,6 +32,7 @@ spec = describe "Abacus" $ do
   newAbacusSpec
   getNumBeadsSpec
   getNumRungsSpec
+  getRungSpec
 
 newAbacusSpec :: Spec
 newAbacusSpec = describe "newAbacusSpec" $ mapM_
@@ -73,4 +74,18 @@ getNumRungsSpec = describe "getNumRungs" $ mapM_
     tenRungs = build 10
     build n = fromJust $ newAbacus 10 n
 
+getRungSpec :: Spec
+getRungSpec = describe "getRung" $ mapM_
+  ( \(desc, rung, expected) -> context desc $ let
+    actual = getRung rung abacus
+    in it ("should be " ++ show expected) $
+      actual `shouldBe` expected
+  )
+  [ ( "0th rung",      0,  Just 2  )
+  , ( "last rung",     2,  Just 5  )
+  , ( "negative rung", -1, Nothing )
+  , ( "too large",     3,  Nothing )
+  ] where
+    abacus = Abacus 10 [2, 3, 5]
+
 --jl