Re: Proposal: Improve the API for TChan, TMVar, and TVar

On 26 March 2011 22:02, wren ng thornton wrote:

On 3/26/11 7:26 AM, Bas van Dijk wrote:

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On 26 March 2011 10:29, wren ng thornton  wrote:

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   modifyTVar :: TVar a ->  (a ->  a) ->  STM ()    modifyTVar' :: TVar a ->  (a ->  a) ->  STM ()

These are highly useful; I use them myself quite often. There's one issue though that has always bugged me about the current API: The types of modifyIORef and modifyMVar don't "line up":

modifyIORef :: IORef a ->  (a ->  a) ->  IO () modifyMVar :: MVar a ->  (a ->  IO (a,b)) ->  IO b

It would have been nicer if modifyMVar lined up with modifyIORef: modifyMVar :: MVar a ->  (a ->  a) ->  IO ()

and have a separate: modifyMVarM :: MVar a ->  (a ->  IO (a,b)) ->  IO b

I guess it's difficult to change that at this stage.

Perhaps the solution at this stage would be to:

(1) add modifyMVarM :: MVar a -> (a -> IO (a,b)) -> IO b (2) deprecate modifyMVar (3) wait a cycle (4) remove modifyMVar (if needed) (5) wait a cycle (if needed) (6) add modifyMVar :: MVar a -> (a -> a) -> IO ()

It'll take forever, but I think it's important to get the names right for this kind of thing rather than letting the inconsistency linger. Of course, this would best be done through a separate proposal IMO.

I agree this should be done in a separate proposal. But while we're talking about it: what's the reason for the extra wait cycle in (5)? Can't we just replace (4),(5) and (6) with a single point where we undeprecate modifyMVar and change its type to the final: MVar a -> (a -> a) -> IO () ? Bas