3 ms·

Could you explain a little more about the complications of nominal subtypes?

• seanmcdirmid 9y ago
  I should have qualified that with the presence of type parameters (nominal subtypes without type parameters are still easy to deal with). Without subtypes, you only unify X and Y (so X = Y), where X and Y are trees with open variables. It turns out X < Y is much harder (semi unification rather than unification). It is basically equivalent to an alias analysis with imperative assignments (subtypes) and fields (type parameters).
  • chillee 9y ago
    You might have seen this already, but there was a thesis on combining subtyping and type inference here: http://www.cl.cam.ac.uk/~sd601/papers/mlsub-preprint.pdf http://www.cl.cam.ac.uk/~sd601/papers/mlsub-preprint.pdf
    • seanmcdirmid 9y ago
      It’s an active research area (less so now than in the 90s), so there is a lot of work on the subject. Nothing in production beyond ordersky’s color type system in scale (and that is completely local). Also, I believe the work you are citing above explores structural subtypes, not nominal ones.