stm: newBroadcastTChan and friends (a proposal, and a question)

[wren ng thornton]

Hello all,

While looking through the pull requests for stm-chans I came across a
discrepancy in the new stm. Namely, we have the following definitions:

* stm == 2.4
    newBroadcastTChan :: STM (TChan a)
    newBroadcastTChan = do
        dummy_hole <- newTVar TNil
        write_hole <- newTVar TNil
        read <- newTVar dummy_hole
        write <- newTVar write_hole
        return (TChan read write)

    newBroadcastTChanIO :: IO (TChan a)
    newBroadcastTChanIO = do
        dummy_hole <- newTVarIO TNil
        write_hole <- newTVarIO TNil
        read <- newTVarIO dummy_hole
        write <- newTVarIO write_hole
        return (TChan read write)

* stm == 2.4.2
    newBroadcastTChan :: STM (TChan a)
    newBroadcastTChan = do
        write_hole <- newTVar TNil
        read <- newTVar (error ...)
        write <- newTVar write_hole
        return (TChan read write)

    newBroadcastTChanIO :: IO (TChan a)
    newBroadcastTChanIO = do
        dummy_hole <- newTVarIO TNil
        write_hole <- newTVarIO TNil
        read <- newTVarIO dummy_hole
        write <- newTVarIO write_hole
        return (TChan read write)

Thus, whoever changed the definition of newBroadcastTChan in 2.4.2 forgot
to change newBroadcastTChanIO to keep it in sync.

PROPOSAL: I propose changing newBroadcastTChanIO to match
newBroadcastTChan. (Deadline: 2 weeks)


QUESTION: Is there any way to re-implement these functions using only the
public API of version 2.3?

-- 
Live well,
~wren