Simon Marlow writes:
I've been thinking about duplicating/replacing Handles for a while. Here's a possible interface:
-- |Returns a duplicate of the original handle, with its own buffer -- and file pointer. The original handle's buffer is flushed, including -- discarding any input data, before the handle is duplicated. hDuplicate :: Handle -> IO Handle -- |Makes the second handle a duplicate of the first handle. The -- second handle will be closed first, if it is not already. hDuplicateTo :: Handle -> Handle -> IO ()
I'm not too sure of the issues here. Some examples that use them would be helpful. The only suggestion I'd make is that the names be something with handle in them: huDupHandle, hDupHandleTo
The remaining questions are: - Should you be allowed to duplicate a Handle which refers to a file opened in WriteMode? Haskell 98 forbids having two Handles pointing to the same file opened for writing, but IMHO it's quite a reasonable thing to do. If we don't allow this, then there needs to be another version of hDuplicateTo which invalidates the original Handle.
Why does Haskell 98 make this restriction (I don't think that the library report says why)? Thanks, Bernie.