[Haskell-cafe] heterogeneous environment

[Heinrich Apfelmus]

Ben wrote:
> while working on an STM-like library, i ran into the issue of trying
> to create a transaction log for reads / writes of heterogeneous
> reference types.  i don't have a good answer to this problem.  the
> problem is twofold : first, the general heterogeneous collection
> problem, and second, connecting a reference to its log.

I've had similar problems while implementing my reactive-banana library. 
The solution is described here

    http://apfelmus.nfshost.com/blog/2011/09/04-vault.html

and also available as a cabal package

    http://hackage.haskell.org/package/vault

Note that the  Vault  data type is probably not quite what you are 
looking for as it represents a whole collection of references. But have 
a look at the type  Data.Vault.Locker  in the vault-0.2 package which I 
have just uploaded to hackage.

Oleg's email describes essentially the same solution.


Best regards,
Heinrich Apfelmus

--
http://apfelmus.nfshost.com