[Haskell-cafe] ACIO versus Execution Contexts

[Simon Peyton-Jones]

| I think it would be nice to summarise the current state of play.  This
really
| needs to be a WiKi.

Thanks for the summary, George. 

| 2.  Which if either of the proposals would the gods responsible for
implementing
| Haskell compilers favour?

Rather than remain completely silent on this topic let me say that 

(a) I'm totally snowed under at the moment, at least partly with GHC
stuff (Template Haskell, GADTs etc); 

(b) there has been so much traffic on this global variable topic that
I've stopped reading it carefully.  This isn't because I think it's
unimportant or boring, but rather because I'm hoping that someone will
eventually emit a summary that really does boil out the main issues, so
that everyone else can benefit from the fruits of your (plural) labours.
The idea would be that everyone else can just read the summary without
reading the thread.  A Wiki would be good.

(c) I have the impression that there's still quite a bit of active
discussion; convergence is not achieved

(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. 

Simon