A verbose and redundant version of an imperative sum in fantasy-land functional style

imperative-sum.js

const Add = x => ({
  x,
  concat: ({x: y}) => x + y,
  fold: f => f(x)
})

const Box = x => ({
  x,
  map: f => Box(f(x)),
  fold: f => f(x)
})

const identity = x => x

Box(1)
  .map(Add)
  .map(
    Box(2)
      .map(Add)
      .fold(identity)
      .concat
  )
  .fold(identity) === 1 + 2