haskell hFlush 没有按照我期望的方式工作

Question

我正在尝试让一个程序使用 hFlush 读取整个文件，以避免我遇到的与惰性 IO 有关的问题。

readHandle <- openFile fileName ReadMode
hSetBuffering readHandle $ BlockBuffering (Just 2048)
fileText <- hGetContents readHandle
hFlush readHandle
hClose readHandle

这只是给我错误:hFlush:非法操作(句柄已关闭)

谁能帮我理解发生了什么

Answer 1

你的期望是错误的。通常，除了显式关闭句柄外，您不应在 hGetContents 调用后使用句柄。来自黑线鳕:

Computation hGetContents hdl returns the list of characters corresponding to the unread portion of the channel or file managed by hdl, which is put into an intermediate state, semi-closed. In this state, hdl is effectively closed, but items are read from hdl on demand and accumulated in a special list returned by hGetContents hdl.