Mob coding through tower of hanoi

homework.cabal

@@ -24,7 +24,7 @@ library
   exposed-modules:
       Homework
       Homework.Ch01.CreditCards
-      Homework.Ch01.TowerOfHanoi
+      Homework.Ch01.Hanoi
       Homework.Ch02.Log
       Homework.Ch02.LogAnalysis
   other-modules:
@@ -34,6 +34,7 @@ library
   ghc-options: -Wall -Werror -Wcompat -Widentities -Wincomplete-patterns -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-home-modules -Wname-shadowing -Wpartial-fields -Wredundant-constraints -Wunused-packages -Wunused-type-patterns
   build-depends:
       base >=4.14 && <5
+    , unordered-containers
   default-language: Haskell2010
 
 executable homework
@@ -53,7 +54,7 @@ test-suite test
   main-is: Spec.hs
   other-modules:
       Homework.Ch01.CreditCardsSpec
-      Homework.Ch01.TowerOfHanoiSpec
+      Homework.Ch01.HanoiSpec
       Paths_homework
   hs-source-dirs:
       test

lib/Homework/Ch01/Hanoi.hs

@@ -0,0 +1,26 @@
+module Homework.Ch01.Hanoi where
+
+import qualified Data.HashMap.Strict as HashMap
+
+newtype Peg = Peg ()
+
+data Move = Move {moveFrom :: String, moveTo :: String} deriving (Eq, Show)
+
+data Disc = Disc {discSize :: Int}
+
+hanoi :: Int -> String -> String -> String -> Either String [Move]
+hanoi numDisks pegLabelA pegLabelB pegLabelC =
+  let _pegs =
+        HashMap.fromList
+          [ (pegLabelA, fillPegWithDiscs),
+            (pegLabelB, []),
+            (pegLabelC, [])
+          ]
+   in Right
+        [ Move "a" "c",
+          Move "a" "b",
+          Move "c" "b"
+        ]
+  where
+    fillPegWithDiscs :: [Disc]
+    fillPegWithDiscs = Disc <$> [1 .. numDisks] -- start here: make sure this is initialized correctly

lib/Homework/Ch01/TowerOfHanoi.hs

@@ -1,16 +0,0 @@
-module Homework.Ch01.TowerOfHanoi where
-
-type Peg = String
-
-type Move = (Peg, Peg)
-
-hanoi :: Integer -> Peg -> Peg -> Peg -> [Move]
-hanoi n x y z = runHanoi [] (reverse $ initStack n) [] []
-  where
-    initStack 0 = []
-    initStack xx = xx : initStack (xx - 1)
-
-    runHanoi moves (itemX : stackX) [] [] = runHanoi ((x, z) : moves) stackX [] [itemX]
-    runHanoi moves (itemX : stackX) [] (itemZ : stackZ)
-      | itemX > itemZ = runHanoi ((x, y) : moves) stackX [itemX] (itemZ : stackZ)
-    runHanoi moves ()

package.yaml

@@ -16,7 +16,8 @@ dependencies:
 
 library:
   source-dirs: lib
-  dependencies: []
+  dependencies:
+  - unordered-containers
 
 executables:
   homework:

test/Homework/Ch01/HanoiSpec.hs

@@ -0,0 +1,14 @@
+module Homework.Ch01.HanoiSpec where
+
+import Homework.Ch01.Hanoi
+import Test.Hspec
+
+spec :: Spec
+spec = describe "hanoi" $ do
+  it "can solve for stack of 2 and three pegs" $ do
+    hanoi 2 "a" "b" "c"
+      `shouldBe` Right
+        [ Move "a" "c",
+          Move "a" "b",
+          Move "c" "b"
+        ]

test/Homework/Ch01/TowerOfHanoiSpec.hs

@@ -1,13 +0,0 @@
-module Homework.Ch01.TowerOfHanoiSpec where
-
-import Homework.Ch01.TowerOfHanoi
-import Test.Hspec
-
-spec :: Spec
-spec = describe "hanoi" $ do
-  it "explodes" $ do
-    hanoi 2 "a" "b" "c"
-      `shouldBe` [ ("a", "c"),
-                   ("a", "b"),
-                   ("c", "b")
-                 ]