The proposal that I like the most is this one:
"Open Data Types and Open Functions"
http://lambda-the-ultimate.org/node/1453
However, it doesn't readily admit using the variants as overlapping
enumerations like John suggested in a previous thread:
http://article.gmane.org/gmane.comp.lang.haskell.cafe/23362
In fact it doesn't really support structural sub-typing at all (the way
that polymorphic variants in Ocaml do), but it does support independent
extension (which PV's don't do).
Dan Doel wrote:
P.S.: Some papers:
http://www.cse.ogi.edu/PacSoft/publications/2000/extensiblerecords.pdf
http://research.microsoft.com/users/daan/download/papers/scopedlabels.pdf
The second actually discusses all the operations on variants and whatnot. The
first just mentions that it's a related topic.
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