Array encoders and decoders about helios

[AdrianRaFo]

All of those will be similar to implement as the List codecs here.

[andrzejressel]

I was trying to implement encoder and decoder for Array, but I've found some issues:

1. A can be neither in nor out
2. When converting list to array using toTypedArray type must be reified.

@extension
interface ArrayEncoderInstance<A> : Encoder<Array<A>> {

  fun encoderA(): Encoder<A>

  override fun Array<A>.encode(): Json =
    JsArray(map { encoderA().run { it.encode() } })

  companion object {
    operator fun <A> invoke(encoderA: Encoder<A>): Encoder<Array<A>> =
      object : ArrayEncoderInstance<A> {
        override fun encoderA(): Encoder<A> = encoderA
      }
  }

}

@extension
interface ArrayDecoderInstance<A> : Decoder<Array<A>> {

  fun decoderA(): Decoder<A>

  override fun decode(value: Json): Either<DecodingError, Array<A>> =
    value.asJsArray().toList()
      .flatMap { arr ->
        arr.value.map { decoderA().decode(it) }
      }.sequence(Either.applicative()).fix().map { it.fix().toTypedArray() }

  companion object {
    operator fun <A> invoke(decoderA: Decoder<A>): Decoder<Array<A>> =
      object : ArrayDecoderInstance<A> {
        override fun decoderA(): Decoder<A> = decoderA
      }
  }

}