Fun(ctional) Programming in JS

PricingInfoRow.ts

import * as O from 'fp-ts/lib/Option'
import * as A from 'fp-ts/lib/Array'
import { sequenceS } from 'fp-ts/lib/Apply'
import { pipe } from 'fp-ts/lib/pipeable'

interface Money { currency: Currency; amount: number }

type PricingInfo = { effectiveDate: Date; price: Money; ticker: string }

enum Currency { USD = "USD", EUR = "EUR", JPY = "JPY", CHF = "CHF", GBP = "GBP", CAD = "CAD", AUD = "AUD", }

const parseRowOption = (row: string[]): O.Option<PricingInfo> => sequenceS(O.option)({
  effectiveDate: pipe(
    row,
    A.lookup(0),
    O.chain(parseDateOption),
  ),
  price: pipe(
    row,
    A.lookup(1),
    O.chain(parseMoneyOption),
  ),
  ticker: pipe(
    row,
    A.lookup(2),
    O.chain(parseTickerOption),
  )
})

// Assumes we have (implement them as an exercise):
// parseDateOption   = (s: string) : O.Option<Date>
// parseMoneyOption  = (s: string) : O.Option<Money>
// it's nitpicky but 'string' should be lowercase here
//                                          vvvvvv
// parseTickerOption = (s: string) : O.Option<string>

original post: https://funprogramming.substack.com/p/functional-programming-in-the-javascript-41b