ramda-partial-application.js

// From http://randycoulman.com/blog/2016/06/07/thinking-in-ramda-partial-application/
const books = [{title: 'foo', year: 1984}, {title: 'bar', year: 1985}]

// original

const publishedInYear = (book, year) => book.year === year
 
const titlesForYear = (books, year) => {
  const selected = filter(book => publishedInYear(book, year), books)
 
  return map(book => book.title, selected)
}

titlesForYear(books, 1985)


// Simplify by returning a function that returns another function

const publishedInYear2 = year => book => book.year === year

const titlesForYear2 = (books, year) => {
  const selected = filter(publishedInYear2(year), books)
 
  return map(book => book.title, selected)
}

titlesForYear2(books, 1985)


// Use partial to acheive the above whilst maintaining a nicer signature for publishedInYear

const publishedInYear3 = (book, year) => book.year === year
 
const titlesForYear3 = (books, year) => {
  const selected = filter(partialRight(publishedInYear3, [year]), books)
 
  return map(book => book.title, selected)
}

titlesForYear3(books, 1985)


// Using curry

const publishedInYear4 = curry((year, book) => book.year === year)
 
const titlesForYear4 = (books, year) => {
  const selected = filter(publishedInYear4(year), books)
 
  return map(book => book.title, selected)
}

titlesForYear4(books, 1985)


// Adding a pipeline

const publishedInYear5= curry((year, book) => book.year === year)
 
const titlesForYear5 = (books, year) =>
  pipe(
    filter(publishedInYear5(year)),
    map(book => book.title)
  )(books)

titlesForYear5(books, 1985)

// Currying again to keep code in the 'data last' ramda convention

const publishedInYear6 = curry((year, book) => book.year === year)
 
const titlesForYear6 = curry((year, books) =>
  pipe(
    filter(publishedInYear6(year)),
    map(book => book.title)
  )(books)
)

titlesForYear6(1985, books)