Type inference for parametric polymorphism is wildly successful, but has always suffered from an embarrassing flaw: polymorphic types are themselves not first class. We present Quick Look, a practical, implemented, and deployable design for impredicative type inference. To demonstrate our claims, we have modified GHC, a production-quality Haskell compiler, to support impredicativity. The changes required are modest, localised, and are fully compatible with GHC's myriad other type system extensions.

@article{SerranoHJV20,
  title = {A quick look at impredicativity},
  author = {Alejandro Serrano and Jurriaan Hage and Simon Peyton Jones and Dimitrios Vytiniotis},
  journal = {Proceedings of the ACM on Programming Languages},
  volume = {4},
  number = {ICFP},
  year = {2020},
  doi = {10.1145/3408971}
}