On Sat, 27 Nov 2004, Benjamin Franksen wrote:
An execution context is a mutable finite map from types to (monomorphic) values. Each IO action implicitly carries exactly one such map and by default passes it on to the actions that follow.
Execution contexts sound a good description of them. Building on your recoding of this, if you have top-level declarations of newMVar / newIORef then how much of this can you do by just keeping a dictionary in a global variable? This should certainly save some of the StateT plumbing; and such declarations are safe, becuase they are affine central (see http://groups.google.com/groups?selm=fa.doh68b9.96sgjd%40ifi.uio.no )
A function is provided to (implicitly) create a new mapping and run a given IO action with the new mapping as its execution context, instead of the default one.
Update the global MVar, do the IO, then reset it?
I am almost sure that even the trick of indexing the dictionary via types (and thus the dependency on Data.Typeable and ghc extensions) can be avoided with a little more effort.
Another global MVar to issue a sequence of unique index keys? Ian -- Ian Stark http://www.ed.ac.uk/~stark LFCS, School of Informatics, The University of Edinburgh, Scotland