New practice exercise food-chain (#780)

Co-authored-by: Angelika Tyborska <[email protected]>

Author: jiegillet

config.json

@@ -2503,6 +2503,22 @@
         ],
         "difficulty": 2
       },
+      {
+        "slug": "food-chain",
+        "name": "Food Chain",
+        "uuid": "7541eeac-169f-4b28-b9d2-7125225b121b",
+        "prerequisites": [
+          "lists",
+          "strings",
+          "pattern-matching",
+          "multiple-clause-functions",
+          "enum"
+        ],
+        "practices": [
+          "strings"
+        ],
+        "difficulty": 5
+      },
       {
         "slug": "affine-cipher",
         "name": "Affine Cipher",

exercises/practice/food-chain/.docs/instructions.md

@@ -0,0 +1,64 @@
+# Description
+
+Generate the lyrics of the song 'I Know an Old Lady Who Swallowed a Fly'.
+
+While you could copy/paste the lyrics,
+or read them from a file, this problem is much more
+interesting if you approach it algorithmically.
+
+This is a [cumulative song](http://en.wikipedia.org/wiki/Cumulative_song) of unknown origin.
+
+This is one of many common variants.
+
+```text
+I know an old lady who swallowed a fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a spider.
+It wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a bird.
+How absurd to swallow a bird!
+She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a cat.
+Imagine that, to swallow a cat!
+She swallowed the cat to catch the bird.
+She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a dog.
+What a hog, to swallow a dog!
+She swallowed the dog to catch the cat.
+She swallowed the cat to catch the bird.
+She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a goat.
+Just opened her throat and swallowed a goat!
+She swallowed the goat to catch the dog.
+She swallowed the dog to catch the cat.
+She swallowed the cat to catch the bird.
+She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a cow.
+I don't know how she swallowed a cow!
+She swallowed the cow to catch the goat.
+She swallowed the goat to catch the dog.
+She swallowed the dog to catch the cat.
+She swallowed the cat to catch the bird.
+She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her.
+She swallowed the spider to catch the fly.
+I don't know why she swallowed the fly. Perhaps she'll die.
+
+I know an old lady who swallowed a horse.
+She's dead, of course!
+```

exercises/practice/food-chain/.formatter.exs

@@ -0,0 +1,4 @@
+# Used by "mix format"
+[
+  inputs: ["{mix,.formatter}.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]

exercises/practice/food-chain/.meta/config.json

@@ -0,0 +1,18 @@
+{
+  "authors": ["jiegillet"],
+  "contributors": [],
+  "files": {
+    "example": [
+      ".meta/example.ex"
+    ],
+    "solution": [
+      "lib/food_chain.ex"
+    ],
+    "test": [
+      "test/food_chain_test.exs"
+    ]
+  },
+  "blurb": "Generate the lyrics of the song 'I Know an Old Lady Who Swallowed a Fly'.",
+  "source": "Wikipedia",
+  "source_url": "http://en.wikipedia.org/wiki/There_Was_an_Old_Lady_Who_Swallowed_a_Fly"
+}

exercises/practice/food-chain/.meta/example.ex

@@ -0,0 +1,54 @@
+defmodule FoodChain do
+  @animals [
+    fly: "I don't know why she swallowed the fly.",
+    spider: "It wriggled and jiggled and tickled inside her.",
+    bird: "How absurd to swallow a bird!",
+    cat: "Imagine that, to swallow a cat!",
+    dog: "What a hog, to swallow a dog!",
+    goat: "Just opened her throat and swallowed a goat!",
+    cow: "I don't know how she swallowed a cow!",
+    horse: "She's dead, of course!"
+  ]
+
+  @doc """
+  Generate consecutive verses of the song 'I Know an Old Lady Who Swallowed a Fly'.
+  """
+  @spec recite(start :: integer, stop :: integer) :: String.t()
+  def recite(start, stop), do: Enum.map_join(start..stop, "\n", &verse/1)
+
+  def verse(1),
+    do: """
+    I know an old lady who swallowed a fly.
+    I don't know why she swallowed the fly. Perhaps she'll die.
+    """
+
+  def verse(8),
+    do: """
+    I know an old lady who swallowed a horse.
+    She's dead, of course!
+    """
+
+  def verse(number) do
+    [{animal, line} | _] =
+      animals =
+      Enum.take(@animals, number)
+      |> Enum.reverse()
+
+    cumulative_lines =
+      Enum.zip(animals, tl(animals))
+      |> Enum.map_join("\n", fn
+        {{:bird, _}, _} ->
+          "She swallowed the bird to catch the spider that wriggled and jiggled and tickled inside her."
+
+        {{a, _}, {b, _}} ->
+          "She swallowed the #{a} to catch the #{b}."
+      end)
+
+    """
+    I know an old lady who swallowed a #{animal}.
+    #{line}
+    #{cumulative_lines}
+    I don't know why she swallowed the fly. Perhaps she'll die.
+    """
+  end
+end

exercises/practice/food-chain/.meta/tests.toml

@@ -0,0 +1,39 @@
+# This is an auto-generated file.
+#
+# Regenerating this file via `configlet sync` will:
+# - Recreate every `description` key/value pair
+# - Recreate every `reimplements` key/value pair, where they exist in problem-specifications
+# - Remove any `include = true` key/value pair (an omitted `include` key implies inclusion)
+# - Preserve any other key/value pair
+#
+# As user-added comments (using the # character) will be removed when this file
+# is regenerated, comments can be added via a `comment` key.
+[751dce68-9412-496e-b6e8-855998c56166]
+description = "fly"
+
+[6c56f861-0c5e-4907-9a9d-b2efae389379]
+description = "spider"
+
+[3edf5f33-bef1-4e39-ae67-ca5eb79203fa]
+description = "bird"
+
+[e866a758-e1ff-400e-9f35-f27f28cc288f]
+description = "cat"
+
+[3f02c30e-496b-4b2a-8491-bc7e2953cafb]
+description = "dog"
+
+[4b3fd221-01ea-46e0-825b-5734634fbc59]
+description = "goat"
+
+[1b707da9-7001-4fac-941f-22ad9c7a65d4]
+description = "cow"
+
+[3cb10d46-ae4e-4d2c-9296-83c9ffc04cdc]
+description = "horse"
+
+[22b863d5-17e4-4d1e-93e4-617329a5c050]
+description = "multiple verses"
+
+[e626b32b-745c-4101-bcbd-3b13456893db]
+description = "full song"

exercises/practice/food-chain/lib/food_chain.ex

@@ -0,0 +1,8 @@
+defmodule FoodChain do
+  @doc """
+  Generate consecutive verses of the song 'I Know an Old Lady Who Swallowed a Fly'.
+  """
+  @spec recite(start :: integer, stop :: integer) :: String.t()
+  def recite(start, stop) do
+  end
+end

exercises/practice/food-chain/mix.exs

@@ -0,0 +1,28 @@
+defmodule FoodChain.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :food_chain,
+      version: "0.1.0",
+      # elixir: "~> 1.8",
+      start_permanent: Mix.env() == :prod,
+      deps: deps()
+    ]
+  end
+
+  # Run "mix help compile.app" to learn about applications.
+  def application do
+    [
+      extra_applications: [:logger]
+    ]
+  end
+
+  # Run "mix help deps" to learn about dependencies.
+  defp deps do
+    [
+      # {:dep_from_hexpm, "~> 0.3.0"},
+      # {:dep_from_git, git: "https://github.com/elixir-lang/my_dep.git", tag: "0.1.0"}
+    ]
+  end
+end