Thanks everyone, I very much appreciate your help, and I think it did help.
I've spent the last few days implementing a substantial chunk of my system
using each of two different techniques. I've ended up going with and ADT
containing functions closed over the 'thing'. This seems to be the
for your convenience, the correct link:
https://lukepalmer.wordpress.com/2010/01/24/haskell-antipattern-existential-typeclass/
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
On 29/01/2013, at 12:43 PM, Bob Hutchison hutch-li...@recursive.ca wrote:
The immediate problem is mapping an input to the system, some json message
containing a reference to the 'thing' (like a key of some kind). I have to
take that reference and find the thing and operate on it. All
Today I thought it was about time to simplify how new 'things' of a certain
kind are added to the system. These things are some a cross between an event
and an assertion of a fact in a rule based system. There are many different
kinds of these things. I already have more than a dozen
If I understand your message well enough, I think you are looking for
GHC's `ExistentialQuantification` extension. Building heterogeneous
collections is a common example of what existential types are useful
for. Take a look at this wiki page [1]; there is an example of how to
accomplish this
On Mon, Jan 28, 2013 at 5:43 PM, Bob Hutchison hutch-li...@recursive.cawrote:
Now, this is how I got caught: it seems to be impossible to have
collections of things with a common type class if they have different
types. How is it that I've written that many lines of code in Haskell and
I'm
