Ramdajs Huffman encoding

huffman.js

/** 
 * By using the RamdaJS library, the entire huffman encoding algorithm is represented with
 * - const
 * - Function application
 * - Function creation (only 4 function closures created, mostly point-free)
 * - Constructing and destructuring of both JSON objects and arrays
 *
 * Thought experiment to verify that a small subset of JavaScript is sufficient to produce sophisticated programs. 
 * Observe no use of if/switch/ternary/for/while, no dot field access, no infix binary operators. 
 */
const ReadMe = {}

const readCount = prop('count')

const mergeTwoNodes = ([left, right]) => [{ count: add(readCount(left), readCount(right)), left, right }]

const mergeToSingleNode = ifElse(
  pipe(length, lt(__, 2)),
  head,
  pipe(
    sortBy(readCount),
    converge(concat, [pipe(take(2), mergeTwoNodes), drop(2)]),
    (nodes) => mergeToSingleNode(nodes)
  )    
)

const huffmanTreeForString = pipe(
  countBy(identity),
  toPairs,
  map(([char, count]) => ({char, count})),
  mergeToSingleNode
)

const codePairsFromHuffmanTree = curry((pathThusFar, {char, left, right}) =>
  ifElse(
    isNil,
    () => concat(
      codePairsFromHuffmanTree(concat(pathThusFar, '0'), left),
      codePairsFromHuffmanTree(concat(pathThusFar, '1'), right),
    ),
    () => [[char, pathThusFar]]    
  )(char)
)

const huffmanCodeFnFromString = pipe(
  huffmanTreeForString,
  codePairsFromHuffmanTree(''),
  fromPairs,
  flip(prop)
)

const huffmanEncodeString = pipe(converge(map, [huffmanCodeFnFromString, split('')]), join(""))

huffmanEncodeString('Hello!')