asyncfail.nim

import asyncdispatch

type KeyNotFoundError* = object of IOError

proc get*(key: string): Future[string] =
  let res = newFuture[string]()
  sleepAsync(500).callback = proc(future: Future[void]) {.closure, gcsafe.} =
    if key != "hello":
      res.fail(newException(KeyNotFoundError, "Key " & key & " is not found"))
    else:
      res.complete("world")
  res

proc getAsync*(key: string): Future[string] {. async .} =
  await sleepAsync(500)
  if key != "hello":
    raise newException(KeyNotFoundError, "Key " & key & " is not found")
  else:
    result = "world"

proc test(): Future[void] {. async .} =
  try:
    let value = await get("unknown")
    assert false
  except KeyNotFoundError:
    assert true
  try: # fail with error
    let value = await getAsync("unknown")
    assert false
  except KeyNotFoundError:
    assert true

waitFor test()