Haskellians, In the attached file i have implemented the bare bones core of the syntax -- pre structural equivalence -- of Milner's presentation of \pi via abstractions and concretions. (There's a minor twist in that the notion of location affords more structure than in Milner's original presentation which i have added to support an ultimate probabilistic interpretation.) The file compiles with ghc as is. If you uncomment the last section, however, you see that to close the loop on the constraints for the agent syntax we hit a typing error. i think this is a hard constraint in Haskell that prevents this level of generality in the specification, but maybe you can see a way around it. i'm certainly no Haskell expert. Best wishes, --greg P.S. The reason for this level of generality is that with it you can close the loop and form a mutual recursion between the types for the syntax of processes and the type of names -- without having that choice predesigned into the structure of processes (or names). i can do this trick in OCaml with recursive modules, but it's definitely not pretty. i was hoping Haskell could make it pretty. -- L.G. Meredith Managing Partner Biosimilarity LLC 505 N 72nd St Seattle, WA 98103 +1 206.650.3740 http://biosimilarity.blogspot.com