The arrow way combined with `DeferredResult` from ...

# arrow

[raulraja]

The arrow way combined with DeferredResult from Spring would be to have your program in terms of IO or Effect so you can run it non blocking. Something along the lines of:

import <http://arrow.effects.IO|arrow.effects.IO>

/** transforms IO into a deferred result **/
fun <A> IO<A>.toDeferredResult(): DeferredResult<A> { 
  val deferredResult = new DeferredResult<ResponseEntity<A>>()
  unsafePerformAsync {
     it.fold(deferredResult.setResult, deferredResult.setResult)
  }
  return deferredResult
}

fun getCustomer(customerId: String): DeferredResult<ResponseEntity<CustomerResponse>> =
  IO { getCustomerService().getCustomer(customerId) }
    .attempt()
    .map {
      it.fold({ 
        ResponseEntity(ErrorResponse(), HttpStatus.INTERNAL_SERVER_ERROR)
      }, { 
        ResponseEntity(CustomerResponse(it) , HttpStatus.OK) 
       })
    }.toDeferredResult()