Inspirations for master's thesis topic

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#1

Hi,

I’m starting my last year of masters degree in CS, and I’d like my thesis to somehow contribute to the PureScript ecosystem. I thought about implementing some advanced type-system features (like type families / GADTs), but I know that such features are deliberately omitted. Perhaps something else (I miss type applications in PS for instance). Is there anything particularly interesting / needed help with that I could contribute to and it could be a topic of a master’s thesis?

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#2

I think constraint kinds and quantified constraints would be more likely to be accepted than type families and GADTs. I can’t think of any features they conflict with, and they would be especially useful in purescript-variant (so that VariantF could internalize evidence other than Functor, like Traversable). It would also allow Functor to imply forall a b. Coercible a b => Coercible (f a) (f b) (essentially representational role). (Some resources on that: Roles for type families (#8177) · Issues · Glasgow Haskell Compiler / GHC · GitLab and Oleg's gists - Should fmap coerce = coerce hold?)

(Right now we do have a kind called Constraint, but constraints cannot be used outside of particular syntactic contexts. Constraint kinds would mean that constraints can be parameters to datatypes, like Dict :: Constraint -> Type would reify the data/evidence for an arbitrary constraint.)

I personally don’t see so much value in type applications, but I don’t have any strong objection to adding them.

Of course it would be good for other core team members to weight in before you start anything, particularly @natefaubion who added polykinds.

These are just some thoughts I have. I’m not sure what the requirements are for a master’s thesis, so you would have to work with your advisor to determine what’s appropriate and what’s feasible.

EDIT: Some more links on roles and coercible in Haskell: roles2 · Wiki · Glasgow Haskell Compiler / GHC · GitLab and How QuantifiedConstraints can let us put join back in Monad - Ryan Scott

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#3

Thank you very much for the feedback!
Does PureScript have roles?

#4

Yes, PureScript has roles: documentation/Roles.md at master · purescript/documentation · GitHub

We were just discussing in Discord the proposal to add forall a b. Coercible a b => Coercible (f a) (f b) as a superclass to Functor, and there seem to be some issues. It’s trickier than I thought. (E.g. Can data Free f a = Pure a | Roll (f (Free f a)) even be made a Functor then?) So that would probably involve a lot more work.