Add food chain (#357)

config.json

@@ -662,6 +662,14 @@
         "practices": [],
         "prerequisites": [],
         "difficulty": 1
+      },
+      {
+        "slug": "food-chain",
+        "name": "Food Chain",
+        "uuid": "fed848ba-5a1d-4b6b-a145-e6d77e40be4d",
+        "practices": [],
+        "prerequisites": [],
+        "difficulty": 2
       }
     ]
   },

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 +1,17 @@
+{
+  "authors": ["blakelewis"],
+  "files": {
+    "solution": [
+      "food-chain.rkt"
+    ],
+    "test": [
+      "food-chain-test.rkt"
+    ],
+    "example": [
+      ".meta/example.rkt"
+    ]
+  },
+  "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/example.rkt

@@ -0,0 +1,52 @@
+#lang racket
+
+(provide recite)
+
+(define spider-action
+  " wriggled and jiggled and tickled inside her")
+
+(define verdict
+  "I don't know why she swallowed the fly. Perhaps she'll die.")
+
+(struct critter (name reaction extra))
+
+(define critters
+  (list
+    (critter "horse" "She's dead, of course!" "")
+    (critter "cow" "I don't know how she swallowed a cow!" "")
+    (critter "goat" "Just opened her throat and swallowed a goat!" "")
+    (critter "dog" "What a hog, to swallow a dog!" "")
+    (critter "cat" "Imagine that, to swallow a cat!" "")
+    (critter "bird" "How absurd to swallow a bird!" "")
+    (critter "spider" (string-append "It" spider-action ".")
+             (string-append " that" spider-action))
+    (critter "fly" verdict "")))
+
+(define (intro c)
+  (list
+    (string-append "I know an old lady who swallowed a "
+                   (critter-name c) ".")
+    (critter-reaction c)))
+
+(define (reason previous c)
+  (string-append "She swallowed the " previous " to catch the "
+		 (critter-name c) (critter-extra c) "."))
+
+(define (verse n)
+  (let* ([cs (drop critters (- (length critters) n))]
+         [start (intro (car cs))])
+    (if (or (eq? cs critters) (null? (cdr cs)))
+      start
+      (for/fold
+        ([v (reverse start)]
+         [previous (critter-name (car cs))]
+         #:result (reverse (cons verdict v)))
+        ([c (cdr cs)])
+        (values (cons (reason previous c) v) (critter-name c))))))
+
+(define (recite start-verse end-verse)
+  (for/fold
+    ([song '()])
+    ([i (in-inclusive-range start-verse end-verse)])
+    (let ([v (if (= i start-verse) (verse i) (cons "" (verse i)))])
+      (append song v))))

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/food-chain-test.rkt

@@ -0,0 +1,148 @@
+#lang racket/base
+
+(require "food-chain.rkt")
+
+(module+ test
+  (require rackunit rackunit/text-ui))
+
+(module+ test
+  (define suite
+    (test-suite "food chain tests"
+
+      (test-equal? "fly"
+        (recite 1 1)
+        '("I know an old lady who swallowed a fly."
+          "I don't know why she swallowed the fly. Perhaps she'll die."))
+
+      (test-equal? "spider"
+        (recite 2 2)
+        '("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."))
+
+      (test-equal? "bird"
+        (recite 3 3)
+        '("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."))
+
+      (test-equal? "cat"
+        (recite 4 4)
+        '("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."))
+
+      (test-equal? "dog"
+        (recite 5 5)
+        '("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."))
+
+      (test-equal? "goat"
+        (recite 6 6)
+        '("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."))
+
+      (test-equal? "cow"
+        (recite 7 7)
+        '("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."))
+
+      (test-equal? "horse"
+        (recite 8 8)
+        '("I know an old lady who swallowed a horse."
+          "She's dead, of course!"))
+
+      (test-equal? "multiple verses"
+        (recite 1 3)
+        '("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."))
+
+      (test-equal? "full song"
+        (recite 1 8)
+        '("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!"))))
+
+  (run-tests suite))

exercises/practice/food-chain/food-chain.rkt

@@ -0,0 +1,6 @@
+#lang racket
+
+(provide recite)
+
+(define (recite start-verse end-verse)
+  (error "Not implemented yet"))