coproducts_optic_vs_immer.ts

import { Option } from '@fp-ts/data/Option'
import * as O from '@fp-ts/data/Option'
import * as S from '@fp-ts/data/String'
import produce from 'immer'
import * as Optic from '@fp-ts/optic'
import * as StringOptic from '@fp-ts/optic/data/String'
import { pipe } from '@fp-ts/data/Function'

// let's say we want to uppercase the second item of the array
interface S {
  readonly a: {
    readonly b: Option<{
      readonly c: ReadonlyArray<Option<string>>
    }>
  }
}

const s: S = {
  a: {
    b: O.some({
      c: [O.none, O.some('aaa'), O.some('bbb')]
    })
  }
}

const _c_1 = Optic.id<S>()
  .at('a')
  .at('b')
  .some()
  .at('c')
  .index(1)
  .some()
  .compose(StringOptic.index(0))

const withOptic = pipe(s, Optic.modify(_c_1)(S.toUpperCase))

const withImmer = produce(s, (draft) => {
  const b = draft.a.b
  if (O.isSome(b)) {
    if (b.value.c.length >= 2 && O.isSome(b.value.c[1])) {
      const s = b.value.c[1].value
      b.value.c[1] = O.some(S.toUpperCase(s.charAt(0)) + s.substring(1))
    }
  }
})

console.log(JSON.stringify(withOptic, null, 2))
console.log(JSON.stringify(withImmer, null, 2))