T.Exact applied to embedded objects

[ericctsf]

trafficstars

T.exact only strips fields of the object at the level it is applied, this makes sense as you wouldn't necessarily want it applying elsewhere.

Is it possible to create a T.deep_exact which applies to all embedded codecs down the tree?

import "mocha"
import chai from "chai"
import * as T from "io-ts"
import * as E from "fp-ts/lib/Either"

const test_base_codec = T.type({
  expected: T.string
})

const test_parent_codec = T.type({
  child: test_base_codec
})

const base_object = {
  expected: 'as usual',
}

const base_object_with_extra_field = {
  ...base_object,
  extra: 'will be stripped'
}

const parent_object = {
  child: base_object
}

const parent_object_with_extra_field = {
  child: base_object_with_extra_field
}

describe.only('io-ts', function () {
  describe('exact', function () {
    it('should strip extra fields from a object when decoding', function () {
      const result = T.exact(test_base_codec).decode(base_object_with_extra_field)
      chai.expect(result).to.deep.equal(E.right(base_object))
    })

    it.only('should strip extra fields from embedded objects when decoding', function () {
      const result = T.deep_exact(test_parent_codec).decode(parent_object_with_extra_field)
      chai.expect(result).to.deep.equal(E.right(parent_object))
    })
  })
})

[mitja-kramberger-cko]

Any suggestions on how to approach this?