Clojure vs Haskell

gist.md

Haskell vs Clojure

The JSON data is in the following format

{
    "Genesis": {
        "1": {
            "1": "In the beginning..." ,
            "2": "..."
        },
        "2": { ... }
    },
    "Exodus": { ... },
    ...
}

In JSON, keys aren't ordered and must be strings.

The goal is to parse the JSON file, order everything correctly (which means parsing the keys into integers), and produce an array that looks like this:

[
    ("Genesis", 1, 1, "In the beginning..")
    ("Genesis", 1, 2, "")
]

The data structure can be a tuple or some new type.

Clojure

(ns versify.core
  (:require [cheshire.core :refer :all])
  (:gen-class))

(def book-order ["Genesis", "Exodus", "Leviticus", "Numbers", "Deuteronomy",
    "Joshua", "Judges", "Ruth", "1 Samuel", "2 Samuel", "1 Kings", "2 Kings",
    "1 Chronicles", "2 Chronicles", "Ezra", "Nehemiah", "Esther", "Job",
    "Psalms", "Proverbs", "Ecclesiastes", "Song of Solomon", "Isaiah",
    "Jeremiah", "Lamentations", "Ezekiel", "Daniel", "Hosea", "Joel", "Amos",
    "Obadiah", "Jonah", "Micah", "Nahum", "Habakkuk", "Zephaniah", "Haggai",
    "Zechariah", "Malachi", "Matthew", "Mark", "Luke", "John", "Acts",
    "Romans", "1 Corinthians", "2 Corinthians", "Galatians", "Ephesians",
    "Philippians", "Colossians", "1 Thessalonians", "2 Thessalonians",
    "1 Timothy", "2 Timothy", "Titus", "Philemon", "Hebrews", "James",
    "1 Peter", "2 Peter", "1 John", "2 John", "3 John", "Jude", "Revelation"])

(defn intify [m]
  (apply assoc (sorted-map)
         (mapcat 
           (fn [[k v]]
             [(read-string k), v]) m)))

(defn get-books [bible]
  (map (fn [book] [book, (bible book)]) book-order))

(defn get-chapters [books]
  (mapcat (fn [[k v]]
         (let [i (intify v)]
           (map (fn [[n c]] [k, n, c]) i))) books))

(defn get-verses [verses]
  (mapcat (fn [[b c d]]
            (let [i (intify d)]
              (map (fn [[v t]] [b, c, v, t]) i))) verses))

(def parse (comp get-verses get-chapters get-books))

(defn -main
  [& args]
  (let [bible (parse-string (slurp "ESV.json"))]
    (first (parse bible))))

Haskell

{-# LANGUAGE OverloadedStrings #-}
module Main where

import Prelude hiding (lookup)
import Data.Aeson (decode, FromJSON)
import Data.Maybe (fromMaybe)
import Data.Aeson.Types
import Control.Applicative ((<$>))
import qualified Data.ByteString.Lazy.Char8 as BS
import Data.Map (Map, toList, fromList, lookup)

bookOrder = ["Genesis", "Exodus", "Leviticus", "Numbers", "Deuteronomy",
    "Joshua", "Judges", "Ruth", "1 Samuel", "2 Samuel", "1 Kings", "2 Kings",
    "1 Chronicles", "2 Chronicles", "Ezra", "Nehemiah", "Esther", "Job",
    "Psalms", "Proverbs", "Ecclesiastes", "Song of Solomon", "Isaiah",
    "Jeremiah", "Lamentations", "Ezekiel", "Daniel", "Hosea", "Joel", "Amos",
    "Obadiah", "Jonah", "Micah", "Nahum", "Habakkuk", "Zephaniah", "Haggai",
    "Zechariah", "Malachi", "Matthew", "Mark", "Luke", "John", "Acts",
    "Romans", "1 Corinthians", "2 Corinthians", "Galatians", "Ephesians",
    "Philippians", "Colossians", "1 Thessalonians", "2 Thessalonians",
    "1 Timothy", "2 Timothy", "Titus", "Philemon", "Hebrews", "James",
    "1 Peter", "2 Peter", "1 John", "2 John", "3 John", "Jude", "Revelation"]

type Verse      = String
newtype Chapter = Chapter (Map String Verse) deriving (Show, Eq, Ord)
newtype Book    = Book (Map String Chapter) deriving (Show, Eq, Ord)
newtype Bible   = Bible (Map String Book) deriving (Show, Eq, Ord)

newtype OrderedChapter = OrderedChapter (Map Int Verse) deriving (Show, Eq, Ord)
newtype OrderedBook    = OrderedBook (Map Int OrderedChapter) deriving (Show, Eq, Ord)
newtype OrderedBible   = OrderedBible (Map String OrderedBook) deriving (Show, Eq, Ord)

instance FromJSON Chapter where
    parseJSON val = Chapter <$> parseJSON val

instance FromJSON Book where
    parseJSON val = Book <$> parseJSON val

instance FromJSON Bible where
    parseJSON val = Bible <$> parseJSON val

getBooks :: OrderedBible -> [(String, OrderedBook)]
getBooks (OrderedBible b) = map (f b) bookOrder
    where f b k = (k, (x k b))
          x k b = case (lookup k b) of
                    Just b -> b
                    Nothing -> error "fail"

getChapters :: [(String, OrderedBook)] -> [(String, Int, OrderedChapter)]
getChapters books = concatMap f books
    where f (bookName, (OrderedBook b))              = map (g bookName) (toList b)
          g bookName (chapterNumber, chapter) = (bookName, chapterNumber, chapter)

getVerses :: [(String, Int, OrderedChapter)] -> [FlatVerse]
getVerses chapters = concatMap f chapters
    where f (bookName, chapterNumber, (OrderedChapter chapter)) = map (g bookName chapterNumber) (toList chapter)
          g bookName chapterNumber (verseNumber, verse)  = FlatVerse {
              text = verse,
              book = bookName,
              chapter = chapterNumber,
              verse = verseNumber}

flattenBible :: OrderedBible -> [FlatVerse]
flattenBible = (getVerses . getChapters . getBooks)

data FlatVerse = FlatVerse { text    :: String
                           , book    :: String
                           , chapter :: Int
                           , verse   :: Int
                           } deriving (Show)

formatVerse :: FlatVerse -> String
formatVerse v = "\"" ++ (text v) ++ "\" - " ++ (book v) ++ " "
                ++ show (chapter v) ++ ":" ++ show (book v)

loadBible :: BS.ByteString -> Bible
loadBible x = do
    let y = decode x :: Maybe Bible 
    case y of
        Just b -> b
        Nothing -> error "mle"

getOrderedBible :: Bible -> OrderedBible
getOrderedBible (Bible bible) = OrderedBible (fromList (c bible))
    where c bible     = map (g bible) bookOrder
          g bible key =  (key, (getOrderedBook book)) where
            book = case lookup key bible of
                Just b -> b
                Nothing -> error "fail"

getOrderedBook :: Book -> OrderedBook
getOrderedBook (Book b) = OrderedBook (fromList (map f (toList b)))
    where f (num, chapter) = (read num :: Int, (getOrderedChapter chapter))

getOrderedChapter :: Chapter -> OrderedChapter
getOrderedChapter (Chapter c) = OrderedChapter (fromList (map f (toList c)))
    where f (num, verse) = (read num :: Int, verse)

main = do
    putStrLn "hey"

    bible <- BS.readFile "ESV.json"
    let b = getOrderedBible (loadBible bible)
        f = flattenBible b
    putStrLn $ show $ length f
    putStrLn $ show $ formatVerse (head f)

Beyond "just give me some tuples", these two programs are not equivalent and the "Haskell vs Clojure" title might be perceived as hyperbolic.

One key thing to point out is that the Haskell program accounts for failure scenarios while the Clojure code does not. This is characteristic of programming styles in both languages. Both will have the same observationally equivalent result when they work properly but when the Clojure code fails it may not be immediately obvious why.

If there is truly no such possibility of a failure condition in this scenario, why bother choosing this as an example of Haskell and Clojure in contrast? Why pick any two languages to compare at all? That's golf. Golf is boring.

The functions for data extraction are the same in the clojure and haskell examples.

@douglasrocha: Not necessarily.

Map.lookup is not "the same" as get (which is secretly hiding in (bible book) in get-book). Map.lookup returns an instance of the type Maybe a where a is some type (e.g. Integer, String, etc.). The value you get will either be Just aValue or Nothing. get on the other hand, only ever returns either an instance of Object or nil. In other words the values you get from Map.lookup can be in different sets while the values you can from get are always from one set.

Haskell solution is type safe

@p-alik 👍