“Yesod开发” devel.hs 中的 fromJust 失败

Question

当我运行“yesod devel”时，它显示“devel.hs: Maybe.fromJust: Nothing

yesod init # created a project bbbb
...
cabal install && yesod devel
...
Registering bbbb-0.0.0...
Starting development server...
Starting devel application
devel.hs: Maybe.fromJust: Nothing

并且 Web 服务器没有侦听端口（我无法在浏览器中打开该网站）

有谁知道如何解决此问题？

我的环境：

• yesod -0.9.4.1
• 光荣的 Glasgow Haskell 编译系统，版本 7.0.3
• Mac OS X 10.6.8

这里是 dist/devel.hs，其中“yesod init”创建：

{-# LANGUAGE PackageImports #-}
import "bbbb" Application (withDevelAppPort)
import Data.Dynamic (fromDynamic)
import Network.Wai.Handler.Warp
    (runSettings, defaultSettings, settingsPort, settingsHost)
import Data.Maybe (fromJust)
import Control.Concurrent (forkIO)
import System.Directory (doesFileExist, removeFile)
import System.Exit (exitSuccess)
import Control.Concurrent (threadDelay)

main :: IO ()
main = do
  putStrLn "Starting devel application"
  wdap <- (return . fromJust . fromDynamic) withDevelAppPort
  forkIO . wdap $ \(port, app) -> runSettings defaultSettings
    { settingsPort = port
    , settingsHost = "0.0.0.0"
    } app
  loop

loop :: IO ()
loop = do
  threadDelay 100000
  e <- doesFileExist "dist/devel-terminate"
  if e then terminateDevel else loop

terminateDevel :: IO ()
terminateDevel = exitSuccess

我上传了 bbbb 目录中的所有文件，Application.hs 是 https://github.com/suztomo/LanguageStudy/blob /master/Haskell/Yesod/bbbb/Application.hs 。

Answer 1

黑暗中的答案：检查你的 cabal 文件，你正在使用 yesod-default 0.5。