How to resolve the algorithm Old lady swallowed a fly step by step in the Haskell programming language

Published on 7 June 2024 03:52 AM
#Haskell

How to resolve the algorithm Old lady swallowed a fly step by step in the Haskell programming language

Table of Contents

Problem Statement

Present a program which emits the lyrics to the song   I Knew an Old Lady Who Swallowed a Fly,   taking advantage of the repetitive structure of the song's lyrics. This song has multiple versions with slightly different lyrics, so all these programs might not emit identical output.

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Old lady swallowed a fly step by step in the Haskell programming language

Both snippets implement the nursery rhyme "There was an old lady who swallowed a fly". The first snippet uses the List package to get the tails of the animals list, which is a list of all the animals that the old lady swallows. It then uses the zipWith function to combine the beginnings of the rhyme with the animals, and the reverse function to reverse the order of the verses. Finally, it uses the concatMap function to concatenate all the verses into a single string, and the putStr function to print the string to the console. The second snippet uses the Map.Strict package to create a map of the animals to their corresponding motivations for swallowing them. It then uses the inits function to get all the initial segments of the menu list, which is a list of the animals that the old lady swallows in order. It then uses the head function to get the first animal in each initial segment, and the tail function to get the rest of the animals in each initial segment. Finally, it uses the intercalate function to concatenate all the initial segments into a single string, and the putStrLn function to print the string to the console.

Source code in the haskell programming language

import Data.List (tails)

animals :: [String]
animals =
  [ "fly.\nI don't know why she swallowed a fly.\nPerhaps she'll die.\n"
  , "spider.\nThat wiggled and jiggled and tickled inside her."
  , "bird.\t\nHow absurd, to swallow a bird."
  , "cat.\t\nImagine that. She swallowed a cat."
  , "dog.\t\nWhat a hog to swallow a dog."
  , "goat.\t\nShe just opened her throat and swallowed a goat."
  , "cow.\nI don't know how she swallowed a cow."
  , "horse.\nShe's dead, of course."
  ]

beginnings :: [String]
beginnings = ("There was an old lady who swallowed a " ++) <$> animals

lastVerse :: [String]
lastVerse =
  reverse
    [ "She swallowed the " ++
     takeWhile (/= '.') y ++ " to catch the " ++ takeWhile (/= '\t') x
    | (x:y:_:_) <- tails animals ]

main :: IO ()
main =
  putStr $
  concatMap unlines $
  zipWith (:) beginnings $ reverse $ ([] :) (tails lastVerse)


import Prelude hiding (lookup)
import Data.Map.Strict (Map, fromList, lookup)
import Data.List (inits, intercalate)
import Data.Maybe (fromMaybe)
import Data.Bool (bool)

main :: IO ()
main = (putStrLn . unlines) (ingestion <$> meal)

meal :: [[String]]
meal = init (reverse <$> tail (inits menu)) ++ [[last menu]]

menu :: [String]
menu = fst <$> courses

courses :: [(String, String)]
courses =
  [ ("fly", "I don't know why she swallowed a fly - perhaps she'll die")
  , ("spider", "It wiggled and jiggled and tickled inside her")
  , ("bird", "How absurd, to swallow a bird")
  , ("cat", "Imagine that. She swallowed a cat")
  , ("dog", "What a hog to swallow a dog")
  , ("goat", "She just opened her throat and swallowed a goat")
  , ("cow", "I don't know how she swallowed a cow")
  , ("horse", "She died, of course")
  ]

ingestion :: [String] -> String
ingestion [] = []
ingestion dishes =
  let appetiser = head dishes
      story = motivation dishes
  in concat
       [ "\nThere was an old lady who swallowed a "
       , appetiser
       , ";\n"
       , reputation appetiser
       , "."
       , bool ("\n\n" ++ story ++ ".") [] (null story)
       ]

motivation :: [String] -> String
motivation [] = []
motivation dishes =
  intercalate ";\n" $
  zipWith
    (\a b -> concat ["She swallowed the ", a, " to catch the ", fullName b])
    dishes
    (tail dishes)

fullName :: String -> String
fullName dish
  | "spider" == dish =
    dish ++ "\nthat " ++ unwords (tail (words (reputation dish)))
  | "fly" == dish = dish ++ ".\n" ++ reputation dish
  | otherwise = dish

reputation :: String -> String
reputation = fromMaybe [] . flip lookup comments

comments :: Map String String
comments = fromList courses

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