implemented setRung

src/Abacus.hs

@@ -30,6 +30,7 @@ module Abacus (
   getNumBeads,
   getNumRungs,
   getRung,
+  setRung,
   ) where
 
 import Data.List (find)
@@ -68,4 +69,26 @@ getRung r a = snd <$> find
   (\(n, _) -> n == r)
   (zip [0..] $ abacusRungs a)
 
+-- | Sets the number of beads slid across a given rung
+setRung
+  :: Int
+  -- ^ The rung number
+  -> Int
+  -- ^ The value being set
+  -> Abacus
+  -- ^ The original state
+  -> Abacus
+  -- ^ The new state
+setRung r v a = a
+  { abacusRungs = zipWith
+    (\n x -> if n == r then v' else x)
+    [0..]
+    (abacusRungs a)
+  }
+  where
+    v'
+      | v < 0             = 0
+      | v > getNumBeads a = getNumBeads a
+      | otherwise         = v
+
 --jl