小编fgh*_*ini的帖子

以下是我们拥有的一个非常常见的模式的简化，其中您有一些重试组合器包装 IO 操作。我想要一些堆栈跟踪，所以我添加了HasCallStack约束，但结果堆栈跟踪并不令人满意：

import Control.Monad (forM_)
import GHC.Stack

httpCall :: HasCallStack => IO ()
httpCall = do
  putStrLn $ prettyCallStack callStack
  print "http resolved"

retry :: HasCallStack => IO () -> IO ()
retry op =
  forM_ [1] $ \i ->
    op

main :: IO ()
main = retry httpCall

堆栈跟踪：

CallStack (from HasCallStack):
  httpCall, called at main.hs:16:14 in main:Main
"http resolved"

我假设HasCallStack约束得到解析main以适应参数类型，retry所以我将约束添加到参数类型：

CallStack (from HasCallStack):
  httpCall, called at main.hs:16:14 in main:Main …