Dan Doel wrote:
Someone already mentioned using Dynamic as an alternate base (for instance, use a Map of dynamics for underlying storage). Of course, the implementation of Dynamic in GHC uses unsafeCoerce, just like ST, so you may not count that. However, using GADTs, you can implement Dynamic safely for a closed universe of types. So you could create a polymorphic reference monad for whatever such universe you wished. Further, if you actually had open GADTs, you could actually add the relevant type-rep constructor for every type you declared. For instance, jhc's implementation of type classes internally uses such a GADT, so one could theoretically make a safe Dynamic, and thus a safe polymorphic reference monad.
Apart from the other inconveniences, all of these solutions involve runtime overhead, which is a shame. Ganesh ============================================================================== Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html ==============================================================================