[Haskell-cafe] ACIO versus Execution Contexts

Adrian Hey ahey at iee.org
Wed Dec 1 07:15:25 EST 2004

On Tuesday 30 Nov 2004 4:01 pm, Simon Peyton-Jones wrote:
> (d) I'm not averse to changing GHC in some way, but big changes (e.g top
> level <-) would need a jolly persuasive argument and solid consensus.
> Smaller changes (e.g. a robust promise about top-level newMVars) are
> easier of course.
> (e) FWIW, as Simon has remarked, we're busy eliminating top-level global
> MVars from GHC.  The really persuasive use I know for them is to
> implement semantically-pure but implementationally impure things like
> memo tables.

Sorry, but aren't these views somewhat contradictory? Either top level
TWIs are needed or they're not. You're indicating that you think they
are needed sometimes (at least top level MVars are) and I do agree.
But if so, it seems sensible to me to try produce a proper framework
for supporting general top-level TWIs properly (and efficiently).

But if top level MVars are all that's on offer I'd settle for that :-)
I can still implement my "oneShot" examples just by passing the top
level MVar as an argument to oneShot rather than having it create its

So yes please, I'd like this.

Adrian Hey

More information about the Haskell-Cafe mailing list