crocksStar.js

import Maybe from 'crocks/Maybe'
import Star from 'crocks/Star'
import prop from 'crocks/Maybe/prop'
import propOr from 'crocks/helpers/propOr'
import resultToMaybe from 'crocks/Maybe/resultToMaybe'
import tryCatch from 'crocks/Result/tryCatch'

const MaybeStar =
  Star(Maybe)

// safeBody :: MaybeStar a b
const safeJSON = MaybeStar(
  resultToMaybe(tryCatch(x => JSON.parse(x)))
)

// safeBody :: MaybeStar b c
const safeBody = MaybeStar(
  prop('body')
)

// safeBody :: MaybeStar a Boolean
const flow =
  safeBody
    .compose(safeJSON)
    .map(propOr(false, 'nice'))

flow
  .runWith({ body: '{"nice": true}' })
//=> Just true

flow
  .runWith({ body: { fast: true } })
//=> Nothing

flow
  .runWith({ payload: '{"nice": true}' })
//=> Nothing

flow
  .runWith({ body: '{"hippy": true}' })
//=> Just false