[Haskell-cafe] Type classes, collections, sum types, closures, and a massive headache

Bob Hutchison hutch-lists at recursive.ca
Thu Jan 31 22:19:41 CET 2013

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 consensus advice. For the record there was a perfectly viable alternative approach based on existential types (http://www.haskell.org/haskellwiki/Heterogenous_collections#Existential_types, thank Taylor, I'd read that and it didn't register… sigh). 

From what I could tell from trying them there's not a lot to choose between the two techniques, some small advantages for each. The existential types technique (despite criticism as an anti-patternhttps://lukepalmer.wordpress.com/2010/01/24/haskell-antipattern-existential-typeclass/, thanks Petr) is surprisingly to my taste… what can I say?

I ended up going with the ADT because I can shove some additional stuff in it, and since there's still a large exploratory aspect to the project this might matter.

Thanks again,

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