apfelmus wrote:
Al Falloon wrote:
OCaml has been getting a lot of mileage from its polymorphic variants
(which allow structural subtyping on sum types) especially on problems
relating to AST transformations and the infamous "expression problem".
Has there been any work on extending Haskell's type system with
structural subtyping?
There's OO'Haskell but I don't know much about it. The problem with
subtyping is that it renders type inference undecidable and is more
limited than parametric polymorphism. It's more like a "syntactic
sugar", you can always explicitly pass around embeddings (a' -> a) and
projections (a -> Maybe a').
Quite.
So another interesting question to ask is 'has anyone proposed any good
syntactic sugar?'
Jules
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