[Haskell-cafe] dangerous inlinePerformIO in Data.Binary(?)

[Stefan O'Rear]

On Fri, Jun 15, 2007 at 06:46:11AM +0100, Duncan Coutts wrote:
> On Fri, 2007-06-15 at 01:03 +0200, Udo Stenzel wrote:
> > The other occurence is:
> > 
> > | unsafeLiftIO :: (Buffer -> IO Buffer) -> Builder
> > | unsafeLiftIO f =  Builder $ \ k buf -> inlinePerformIO $ do
> > |     buf' <- f buf
> > |     return (k buf')
> > 
> > which might be safe, since 'f buf' cannot float out of the lambda which
> > binds 'buf', but still, all this stuff is inlined, something constant
> > might get plugged in the place of buf and the result might be floated
> > out to give us an even harder to find Heisenbug.
> 
> I think this is safe because of the continuation k. In the Builder
> monoid, the continuation takes the place of the IO state token that gets
> single threaded through everything.

That's only safe if every function which passes an initial continuation
(runBuilder etc) is NOINLINE - exactly the sort of global requirement
that is far too easy to break if not documented.

Stefan