food-chain: Rewrite tests and add working stub solution.

exercises/food-chain/HINTS.md

@@ -0,0 +1,19 @@
+## 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.
+- Generalize your solution, allowing the lady to swallow other things.
+
+Take your time.
+
+Change one thing at a time and check if your solution still passes the tests.
+
+Have fun!

exercises/food-chain/src/Example.hs

@@ -15,7 +15,7 @@ animalNames = listArray (Fly, Horse) $ map showLower [Fly ..]
                       in (toLower h : t)
 
 song :: String
-song = unlines $ map verse [Fly ..]
+song = init . unlines $ map verse [Fly ..]
 
 verse :: Animal -> String
 verse animal = swallow animal ++ unlines (map catches prey)

exercises/food-chain/src/FoodChain.hs

@@ -1,4 +1,54 @@
 module FoodChain (song) where
 
 song :: String
-song = undefined
+song =
+    "I know an old lady who swallowed a fly.\n\
+    \I don't know why she swallowed the fly. Perhaps she'll die.\n\
+    \\n\
+    \I know an old lady who swallowed a spider.\n\
+    \It wriggled and jiggled and tickled inside her.\n\
+    \She swallowed the spider to catch the fly.\n\
+    \I don't know why she swallowed the fly. Perhaps she'll die.\n\
+    \\n\
+    \I know an old lady who swallowed a bird.\n\
+    \How absurd to swallow a bird!\n\
+    \She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n\
+    \She swallowed the spider to catch the fly.\n\
+    \I don't know why she swallowed the fly. Perhaps she'll die.\n\
+    \\n\
+    \I know an old lady who swallowed a cat.\n\
+    \Imagine that, to swallow a cat!\n\
+    \She swallowed the cat to catch the bird.\n\
+    \She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n\
+    \She swallowed the spider to catch the fly.\n\
+    \I don't know why she swallowed the fly. Perhaps she'll die.\n\
+    \\n\
+    \I know an old lady who swallowed a dog.\n\
+    \What a hog, to swallow a dog!\n\
+    \She swallowed the dog to catch the cat.\n\
+    \She swallowed the cat to catch the bird.\n\
+    \She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n\
+    \She swallowed the spider to catch the fly.\n\
+    \I don't know why she swallowed the fly. Perhaps she'll die.\n\
+    \\n\
+    \I know an old lady who swallowed a goat.\n\
+    \Just opened her throat and swallowed a goat!\n\
+    \She swallowed the goat to catch the dog.\n\
+    \She swallowed the dog to catch the cat.\n\
+    \She swallowed the cat to catch the bird.\n\
+    \She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n\
+    \She swallowed the spider to catch the fly.\n\
+    \I don't know why she swallowed the fly. Perhaps she'll die.\n\
+    \\n\
+    \I know an old lady who swallowed a cow.\n\
+    \I don't know how she swallowed a cow!\n\
+    \She swallowed the cow to catch the goat.\n\
+    \She swallowed the goat to catch the dog.\n\
+    \She swallowed the dog to catch the cat.\n\
+    \She swallowed the cat to catch the bird.\n\
+    \She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n\
+    \She swallowed the spider to catch the fly.\n\
+    \I don't know why she swallowed the fly. Perhaps she'll die.\n\
+    \\n\
+    \I know an old lady who swallowed a horse.\n\
+    \She's dead, of course!\n"

exercises/food-chain/test/Tests.hs

@@ -1,3 +1,4 @@
+import Data.Function     (on)
 import Test.Hspec        (Spec, describe, it, shouldBe)
 import Test.Hspec.Runner (configFastFail, defaultConfig, hspecWith)
 
@@ -8,56 +9,79 @@ main = hspecWith defaultConfig {configFastFail = True} specs
 
 specs :: Spec
 specs = describe "food-chain" $
-          it "song" $ song `shouldBe` expected
+
+          describe "song" $ 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" $ song `shouldBe` lyrics
   where
-    expected = "I know an old lady who swallowed a fly.\n\
-               \I don't know why she swallowed the fly. Perhaps she'll die.\n\
-               \\n\
-               \I know an old lady who swallowed a spider.\n\
-               \It wriggled and jiggled and tickled inside her.\n\
-               \She swallowed the spider to catch the fly.\n\
-               \I don't know why she swallowed the fly. Perhaps she'll die.\n\
-               \\n\
-               \I know an old lady who swallowed a bird.\n\
-               \How absurd to swallow a bird!\n\
-               \She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n\
-               \She swallowed the spider to catch the fly.\n\
-               \I don't know why she swallowed the fly. Perhaps she'll die.\n\
-               \\n\
-               \I know an old lady who swallowed a cat.\n\
-               \Imagine that, to swallow a cat!\n\
-               \She swallowed the cat to catch the bird.\n\
-               \She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n\
-               \She swallowed the spider to catch the fly.\n\
-               \I don't know why she swallowed the fly. Perhaps she'll die.\n\
-               \\n\
-               \I know an old lady who swallowed a dog.\n\
-               \What a hog, to swallow a dog!\n\
-               \She swallowed the dog to catch the cat.\n\
-               \She swallowed the cat to catch the bird.\n\
-               \She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n\
-               \She swallowed the spider to catch the fly.\n\
-               \I don't know why she swallowed the fly. Perhaps she'll die.\n\
-               \\n\
-               \I know an old lady who swallowed a goat.\n\
-               \Just opened her throat and swallowed a goat!\n\
-               \She swallowed the goat to catch the dog.\n\
-               \She swallowed the dog to catch the cat.\n\
-               \She swallowed the cat to catch the bird.\n\
-               \She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n\
-               \She swallowed the spider to catch the fly.\n\
-               \I don't know why she swallowed the fly. Perhaps she'll die.\n\
-               \\n\
-               \I know an old lady who swallowed a cow.\n\
-               \I don't know how she swallowed a cow!\n\
-               \She swallowed the cow to catch the goat.\n\
-               \She swallowed the goat to catch the dog.\n\
-               \She swallowed the dog to catch the cat.\n\
-               \She swallowed the cat to catch the bird.\n\
-               \She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n\
-               \She swallowed the spider to catch the fly.\n\
-               \I don't know why she swallowed the fly. Perhaps she'll die.\n\
-               \\n\
-               \I know an old lady who swallowed a horse.\n\
-               \She's dead, of course!\n\
-               \\n"
+
+    lineAssertions = (go shouldBe `on` zip [1 :: Int ..] . lines) song lyrics
+
+    go _    []     []  = []
+    go f (x:xs)    []  = f (Just x) Nothing  : go f xs []
+    go f    []  (y:ys) = f Nothing  (Just y) : go f [] ys
+    go f (x:xs) (y:ys) = f (Just x) (Just y) : go f xs ys
+
+-- Lyrics extracted from `exercism/x-common` on 2016-09-21.
+
+lyrics :: String
+lyrics =
+    "I know an old lady who swallowed a fly.\n\
+    \I don't know why she swallowed the fly. Perhaps she'll die.\n\
+    \\n\
+    \I know an old lady who swallowed a spider.\n\
+    \It wriggled and jiggled and tickled inside her.\n\
+    \She swallowed the spider to catch the fly.\n\
+    \I don't know why she swallowed the fly. Perhaps she'll die.\n\
+    \\n\
+    \I know an old lady who swallowed a bird.\n\
+    \How absurd to swallow a bird!\n\
+    \She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n\
+    \She swallowed the spider to catch the fly.\n\
+    \I don't know why she swallowed the fly. Perhaps she'll die.\n\
+    \\n\
+    \I know an old lady who swallowed a cat.\n\
+    \Imagine that, to swallow a cat!\n\
+    \She swallowed the cat to catch the bird.\n\
+    \She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n\
+    \She swallowed the spider to catch the fly.\n\
+    \I don't know why she swallowed the fly. Perhaps she'll die.\n\
+    \\n\
+    \I know an old lady who swallowed a dog.\n\
+    \What a hog, to swallow a dog!\n\
+    \She swallowed the dog to catch the cat.\n\
+    \She swallowed the cat to catch the bird.\n\
+    \She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n\
+    \She swallowed the spider to catch the fly.\n\
+    \I don't know why she swallowed the fly. Perhaps she'll die.\n\
+    \\n\
+    \I know an old lady who swallowed a goat.\n\
+    \Just opened her throat and swallowed a goat!\n\
+    \She swallowed the goat to catch the dog.\n\
+    \She swallowed the dog to catch the cat.\n\
+    \She swallowed the cat to catch the bird.\n\
+    \She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n\
+    \She swallowed the spider to catch the fly.\n\
+    \I don't know why she swallowed the fly. Perhaps she'll die.\n\
+    \\n\
+    \I know an old lady who swallowed a cow.\n\
+    \I don't know how she swallowed a cow!\n\
+    \She swallowed the cow to catch the goat.\n\
+    \She swallowed the goat to catch the dog.\n\
+    \She swallowed the dog to catch the cat.\n\
+    \She swallowed the cat to catch the bird.\n\
+    \She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.\n\
+    \She swallowed the spider to catch the fly.\n\
+    \I don't know why she swallowed the fly. Perhaps she'll die.\n\
+    \\n\
+    \I know an old lady who swallowed a horse.\n\
+    \She's dead, of course!\n"