Add new practice exercise food-chain (#709)

config.json

@@ -1340,6 +1340,20 @@
         ],
         "difficulty": 6
       },
+      {
+        "slug": "food-chain",
+        "name": "Food Chain",
+        "uuid": "40e735ba-0bc7-436e-9c5f-5a8abdf8c436",
+        "practices": [],
+        "prerequisites": [
+          "strings",
+          "lists",
+          "tuples",
+          "pattern-matching",
+          "let"
+        ],
+        "difficulty": 4
+      },
       {
         "slug": "knapsack",
         "name": "Knapsack",

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

@@ -0,0 +1,64 @@
+# Instructions
+
+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][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!
+```
+
+[cumulative-song]: https://en.wikipedia.org/wiki/Cumulative_song

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

@@ -0,0 +1,19 @@
+{
+  "authors": [
+    "jiegillet"
+  ],
+  "files": {
+    "solution": [
+      "src/FoodChain.elm"
+    ],
+    "test": [
+      "tests/Tests.elm"
+    ],
+    "example": [
+      ".meta/src/FoodChain.example.elm"
+    ]
+  },
+  "blurb": "Generate the lyrics of the song 'I Know an Old Lady Who Swallowed a Fly'.",
+  "source": "Wikipedia",
+  "source_url": "https://en.wikipedia.org/wiki/There_Was_an_Old_Lady_Who_Swallowed_a_Fly"
+}

exercises/practice/food-chain/.meta/src/FoodChain.example.elm

@@ -0,0 +1,63 @@
+module FoodChain exposing (recite)
+
+
+recite : Int -> Int -> String
+recite startVerse endVerse =
+    List.range startVerse endVerse
+        |> List.map (verseLines >> String.join "\n")
+        |> String.join "\n\n"
+
+
+songData : List ( String, String )
+songData =
+    [ ( "horse", "She's dead, of course!" )
+    , ( "cow", "I don't know how she swallowed a cow!" )
+    , ( "goat", "Just opened her throat and swallowed a goat!" )
+    , ( "dog", "What a hog, to swallow a dog!" )
+    , ( "cat", "Imagine that, to swallow a cat!" )
+    , ( "bird", "How absurd to swallow a bird!" )
+    , ( "spider", "It wriggled and jiggled and tickled inside her." )
+    , ( "fly", "I don't know why she swallowed the fly. Perhaps she'll die." )
+    ]
+
+
+numberOfVerses : Int
+numberOfVerses =
+    8
+
+
+verseLines : Int -> List String
+verseLines n =
+    let
+        line animal =
+            "I know an old lady who swallowed a " ++ animal ++ "."
+    in
+    case List.drop (numberOfVerses - n) songData of
+        [] ->
+            []
+
+        ( "horse" as animal, phrase ) :: _ ->
+            [ line animal, phrase ]
+
+        ( animal, phrase ) :: rest ->
+            line animal :: phrase :: escalation animal rest
+
+
+escalation : String -> List ( String, String ) -> List String
+escalation animal remainingData =
+    let
+        line nextAnimal =
+            "She swallowed the " ++ animal ++ " to catch the " ++ nextAnimal ++ "."
+    in
+    case remainingData of
+        [] ->
+            []
+
+        [ ( lastAnimal, lastPhrase ) ] ->
+            [ line lastAnimal, lastPhrase ]
+
+        ( "spider" as nextAnimal, _ ) :: rest ->
+            line "spider that wriggled and jiggled and tickled inside her" :: escalation nextAnimal rest
+
+        ( nextAnimal, _ ) :: rest ->
+            line nextAnimal :: escalation nextAnimal rest

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

@@ -0,0 +1,40 @@
+# 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/elm.json

@@ -0,0 +1,29 @@
+{
+    "type": "application",
+    "source-directories": [
+        "src"
+    ],
+    "elm-version": "0.19.1",
+    "dependencies": {
+        "direct": {
+            "elm/core": "1.0.5",
+            "elm/json": "1.1.3",
+            "elm/parser": "1.1.0",
+            "elm/random": "1.0.0",
+            "elm/regex": "1.0.0",
+            "elm/time": "1.0.0"
+        },
+        "indirect": {}
+    },
+    "test-dependencies": {
+        "direct": {
+            "elm-explorations/test": "2.1.0",
+            "rtfeldman/elm-iso8601-date-strings": "1.1.4"
+        },
+        "indirect": {
+            "elm/bytes": "1.0.8",
+            "elm/html": "1.0.0",
+            "elm/virtual-dom": "1.0.3"
+        }
+    }
+}

exercises/practice/food-chain/src/FoodChain.elm

@@ -0,0 +1,6 @@
+module FoodChain exposing (recite)
+
+
+recite : Int -> Int -> String
+recite startVerse endVerse =
+    Debug.todo "Please implement recite"