import strutils, sockets, asynchttpserver
from asyncdispatch import Future

proc handler(request: Request): Future[void] {.closure, gcsafe.} =
  echo "hello"

var server = newAsyncHttpServer()
discard server.serve(Port(80), handler, "")

================================================================================================================
main.nim(8, 14) Error: type mismatch: got (AsyncHttpServer, Port, proc (Request): Future[void]{.closure, gcsafe, locks: <unknown>.}, string)
but expected one of:
asynchttpserver.serve(server: AsyncHttpServer, port: Port, callback: proc (Request): Future[void]{.closure, gcsafe.}, address: string): Future[void]