export interface OptionC<C extends t.Mixed> extends t.Type<Option<t.TypeOf<C>>, OptionOutput<t.OutputOf<C>>, unknown> {}

import { option } from 'io-ts-types/lib/option'
import { right } from 'fp-ts/lib/Either'
import { none, some } from 'fp-ts/lib/Option'
import * as t from 'io-ts'
import { PathReporter } from 'io-ts/lib/PathReporter'

const T = option(t.number)

assert.deepStrictEqual(T.decode(none), right(none))
assert.deepStrictEqual(T.decode(some(1)), right(some(1)))
assert.deepStrictEqual(PathReporter.report(T.decode(some('a'))), [
  'Invalid value "a" supplied to : Option<number>/1: Some<number>/value: number'
])

export type NoneOutput = t.OutputOf<typeof None>

export type OptionOutput<A> = NoneOutput | SomeOutput<A>

export type SomeOutput<A> = { _tag: 'Some'; value: A }

export function option<C extends t.Mixed>(codec: C, name: string = `Option<${codec.name}>`): OptionC<C> { ... }