house: Fix tests to match x-common and add working stub solution.

exercises/house/HINTS.md

@@ -0,0 +1,18 @@
+## Hints
+
+This exercise is about [code refactoring](https://en.wikipedia.org/wiki/Refactoring),
+so we are providing you with a solution that already passes the tests.
+
+The challenge is to rewrite it until you are proud of it, and learn
+something in the process.
+
+If you don't know where to start, here are some ideas:
+
+- Try to reduce repetition to a minimum.
+- Try to make the code readable.
+
+Take your time.
+
+Change one thing at a time and check if your solution still passes the tests.
+
+Have fun!

exercises/house/src/Example.hs

@@ -1,7 +1,9 @@
 module House (rhyme) where
 
+import Data.List (intercalate)
+
 rhyme :: String
-rhyme = unlines $ map ("This is " ++) $ scanl1 f pieces
+rhyme = intercalate "\n" $ map ("This is " ++) $ scanl1 f pieces
   where f tail' piece = piece ++ ' ' : tail'
 
 pieces :: [String]

exercises/house/src/House.hs

@@ -1,4 +1,92 @@
 module House (rhyme) where
 
 rhyme :: String
-rhyme = undefined
+rhyme = "This is the house that Jack built.\n\
+        \\n\
+        \This is the malt\n\
+        \that lay in the house that Jack built.\n\
+        \\n\
+        \This is the rat\n\
+        \that ate the malt\n\
+        \that lay in the house that Jack built.\n\
+        \\n\
+        \This is the cat\n\
+        \that killed the rat\n\
+        \that ate the malt\n\
+        \that lay in the house that Jack built.\n\
+        \\n\
+        \This is the dog\n\
+        \that worried the cat\n\
+        \that killed the rat\n\
+        \that ate the malt\n\
+        \that lay in the house that Jack built.\n\
+        \\n\
+        \This is the cow with the crumpled horn\n\
+        \that tossed the dog\n\
+        \that worried the cat\n\
+        \that killed the rat\n\
+        \that ate the malt\n\
+        \that lay in the house that Jack built.\n\
+        \\n\
+        \This is the maiden all forlorn\n\
+        \that milked the cow with the crumpled horn\n\
+        \that tossed the dog\n\
+        \that worried the cat\n\
+        \that killed the rat\n\
+        \that ate the malt\n\
+        \that lay in the house that Jack built.\n\
+        \\n\
+        \This is the man all tattered and torn\n\
+        \that kissed the maiden all forlorn\n\
+        \that milked the cow with the crumpled horn\n\
+        \that tossed the dog\n\
+        \that worried the cat\n\
+        \that killed the rat\n\
+        \that ate the malt\n\
+        \that lay in the house that Jack built.\n\
+        \\n\
+        \This is the priest all shaven and shorn\n\
+        \that married the man all tattered and torn\n\
+        \that kissed the maiden all forlorn\n\
+        \that milked the cow with the crumpled horn\n\
+        \that tossed the dog\n\
+        \that worried the cat\n\
+        \that killed the rat\n\
+        \that ate the malt\n\
+        \that lay in the house that Jack built.\n\
+        \\n\
+        \This is the rooster that crowed in the morn\n\
+        \that woke the priest all shaven and shorn\n\
+        \that married the man all tattered and torn\n\
+        \that kissed the maiden all forlorn\n\
+        \that milked the cow with the crumpled horn\n\
+        \that tossed the dog\n\
+        \that worried the cat\n\
+        \that killed the rat\n\
+        \that ate the malt\n\
+        \that lay in the house that Jack built.\n\
+        \\n\
+        \This is the farmer sowing his corn\n\
+        \that kept the rooster that crowed in the morn\n\
+        \that woke the priest all shaven and shorn\n\
+        \that married the man all tattered and torn\n\
+        \that kissed the maiden all forlorn\n\
+        \that milked the cow with the crumpled horn\n\
+        \that tossed the dog\n\
+        \that worried the cat\n\
+        \that killed the rat\n\
+        \that ate the malt\n\
+        \that lay in the house that Jack built.\n\
+        \\n\
+        \This is the horse and the hound and the horn\n\
+        \that belonged to the farmer sowing his corn\n\
+        \that kept the rooster that crowed in the morn\n\
+        \that woke the priest all shaven and shorn\n\
+        \that married the man all tattered and torn\n\
+        \that kissed the maiden all forlorn\n\
+        \that milked the cow with the crumpled horn\n\
+        \that tossed the dog\n\
+        \that worried the cat\n\
+        \that killed the rat\n\
+        \that ate the malt\n\
+        \that lay in the house that Jack built.\n"

exercises/house/test/Tests.hs

@@ -1,4 +1,5 @@
-import Test.Hspec        (Spec, describe, it, shouldBe)
+import Control.Monad     (unless)
+import Test.Hspec        (Spec, describe, expectationFailure, it, shouldBe)
 import Test.Hspec.Runner (configFastFail, defaultConfig, hspecWith)
 
 import House (rhyme)
@@ -8,96 +9,121 @@ main = hspecWith defaultConfig {configFastFail = True} specs
 
 specs :: Spec
 specs = describe "house" $
-          it "rhyme" $ rhyme `shouldBe` expected
+
+          describe "rhyme" $ do
+
+            -- First we test the input, line by line, to give more
+            -- useful error messages.
+
+            it "matches lines" $ sequence_ lineAssertions
+
+            -- Finally, because testing lines we are unable
+            -- to detect a missing newline at the end of the
+            -- lyrics, we test the full song.
+
+            it "matches full song" $ rhyme `shouldBe` lyrics
   where
-    expected = "This is the house that Jack built.\n\
-               \\n\
-               \This is the malt\n\
-               \that lay in the house that Jack built.\n\
-               \\n\
-               \This is the rat\n\
-               \that ate the malt\n\
-               \that lay in the house that Jack built.\n\
-               \\n\
-               \This is the cat\n\
-               \that killed the rat\n\
-               \that ate the malt\n\
-               \that lay in the house that Jack built.\n\
-               \\n\
-               \This is the dog\n\
-               \that worried the cat\n\
-               \that killed the rat\n\
-               \that ate the malt\n\
-               \that lay in the house that Jack built.\n\
-               \\n\
-               \This is the cow with the crumpled horn\n\
-               \that tossed the dog\n\
-               \that worried the cat\n\
-               \that killed the rat\n\
-               \that ate the malt\n\
-               \that lay in the house that Jack built.\n\
-               \\n\
-               \This is the maiden all forlorn\n\
-               \that milked the cow with the crumpled horn\n\
-               \that tossed the dog\n\
-               \that worried the cat\n\
-               \that killed the rat\n\
-               \that ate the malt\n\
-               \that lay in the house that Jack built.\n\
-               \\n\
-               \This is the man all tattered and torn\n\
-               \that kissed the maiden all forlorn\n\
-               \that milked the cow with the crumpled horn\n\
-               \that tossed the dog\n\
-               \that worried the cat\n\
-               \that killed the rat\n\
-               \that ate the malt\n\
-               \that lay in the house that Jack built.\n\
-               \\n\
-               \This is the priest all shaven and shorn\n\
-               \that married the man all tattered and torn\n\
-               \that kissed the maiden all forlorn\n\
-               \that milked the cow with the crumpled horn\n\
-               \that tossed the dog\n\
-               \that worried the cat\n\
-               \that killed the rat\n\
-               \that ate the malt\n\
-               \that lay in the house that Jack built.\n\
-               \\n\
-               \This is the rooster that crowed in the morn\n\
-               \that woke the priest all shaven and shorn\n\
-               \that married the man all tattered and torn\n\
-               \that kissed the maiden all forlorn\n\
-               \that milked the cow with the crumpled horn\n\
-               \that tossed the dog\n\
-               \that worried the cat\n\
-               \that killed the rat\n\
-               \that ate the malt\n\
-               \that lay in the house that Jack built.\n\
-               \\n\
-               \This is the farmer sowing his corn\n\
-               \that kept the rooster that crowed in the morn\n\
-               \that woke the priest all shaven and shorn\n\
-               \that married the man all tattered and torn\n\
-               \that kissed the maiden all forlorn\n\
-               \that milked the cow with the crumpled horn\n\
-               \that tossed the dog\n\
-               \that worried the cat\n\
-               \that killed the rat\n\
-               \that ate the malt\n\
-               \that lay in the house that Jack built.\n\
-               \\n\
-               \This is the horse and the hound and the horn\n\
-               \that belonged to the farmer sowing his corn\n\
-               \that kept the rooster that crowed in the morn\n\
-               \that woke the priest all shaven and shorn\n\
-               \that married the man all tattered and torn\n\
-               \that kissed the maiden all forlorn\n\
-               \that milked the cow with the crumpled horn\n\
-               \that tossed the dog\n\
-               \that worried the cat\n\
-               \that killed the rat\n\
-               \that ate the malt\n\
-               \that lay in the house that Jack built.\n\
-               \\n\
-               \"
+
+    lineAssertions = zipWith checkLine [1 :: Int ..] $ zipMaybe (lines rhyme) (lines lyrics)
+
+    checkLine lineno (got, want) =
+      unless (got == want) $
+        expectationFailure $ "mismatch at line " ++ show lineno ++ "\nexpected: " ++ show want ++ "\n but got: " ++ show got
+
+    zipMaybe    []     []  = []
+    zipMaybe (x:xs)    []  = (Just x , Nothing) : zipMaybe xs []
+    zipMaybe    []  (y:ys) = (Nothing, Just y ) : zipMaybe [] ys
+    zipMaybe (x:xs) (y:ys) = (Just x , Just y ) : zipMaybe xs ys
+
+-- Lyrics extracted from `exercism/x-common` on 2016-09-23.
+
+lyrics :: String
+lyrics = "This is the house that Jack built.\n\
+         \\n\
+         \This is the malt\n\
+         \that lay in the house that Jack built.\n\
+         \\n\
+         \This is the rat\n\
+         \that ate the malt\n\
+         \that lay in the house that Jack built.\n\
+         \\n\
+         \This is the cat\n\
+         \that killed the rat\n\
+         \that ate the malt\n\
+         \that lay in the house that Jack built.\n\
+         \\n\
+         \This is the dog\n\
+         \that worried the cat\n\
+         \that killed the rat\n\
+         \that ate the malt\n\
+         \that lay in the house that Jack built.\n\
+         \\n\
+         \This is the cow with the crumpled horn\n\
+         \that tossed the dog\n\
+         \that worried the cat\n\
+         \that killed the rat\n\
+         \that ate the malt\n\
+         \that lay in the house that Jack built.\n\
+         \\n\
+         \This is the maiden all forlorn\n\
+         \that milked the cow with the crumpled horn\n\
+         \that tossed the dog\n\
+         \that worried the cat\n\
+         \that killed the rat\n\
+         \that ate the malt\n\
+         \that lay in the house that Jack built.\n\
+         \\n\
+         \This is the man all tattered and torn\n\
+         \that kissed the maiden all forlorn\n\
+         \that milked the cow with the crumpled horn\n\
+         \that tossed the dog\n\
+         \that worried the cat\n\
+         \that killed the rat\n\
+         \that ate the malt\n\
+         \that lay in the house that Jack built.\n\
+         \\n\
+         \This is the priest all shaven and shorn\n\
+         \that married the man all tattered and torn\n\
+         \that kissed the maiden all forlorn\n\
+         \that milked the cow with the crumpled horn\n\
+         \that tossed the dog\n\
+         \that worried the cat\n\
+         \that killed the rat\n\
+         \that ate the malt\n\
+         \that lay in the house that Jack built.\n\
+         \\n\
+         \This is the rooster that crowed in the morn\n\
+         \that woke the priest all shaven and shorn\n\
+         \that married the man all tattered and torn\n\
+         \that kissed the maiden all forlorn\n\
+         \that milked the cow with the crumpled horn\n\
+         \that tossed the dog\n\
+         \that worried the cat\n\
+         \that killed the rat\n\
+         \that ate the malt\n\
+         \that lay in the house that Jack built.\n\
+         \\n\
+         \This is the farmer sowing his corn\n\
+         \that kept the rooster that crowed in the morn\n\
+         \that woke the priest all shaven and shorn\n\
+         \that married the man all tattered and torn\n\
+         \that kissed the maiden all forlorn\n\
+         \that milked the cow with the crumpled horn\n\
+         \that tossed the dog\n\
+         \that worried the cat\n\
+         \that killed the rat\n\
+         \that ate the malt\n\
+         \that lay in the house that Jack built.\n\
+         \\n\
+         \This is the horse and the hound and the horn\n\
+         \that belonged to the farmer sowing his corn\n\
+         \that kept the rooster that crowed in the morn\n\
+         \that woke the priest all shaven and shorn\n\
+         \that married the man all tattered and torn\n\
+         \that kissed the maiden all forlorn\n\
+         \that milked the cow with the crumpled horn\n\
+         \that tossed the dog\n\
+         \that worried the cat\n\
+         \that killed the rat\n\
+         \that ate the malt\n\
+         \that lay in the house that Jack built.\n"