That is outrageous. It also cannot be blamed on Hindley Milner. While HM in theory has exponential worst case time, the constructs to trigger it for OCaml and Standard ML are far more complex, carefully constructed and never occur in practice.
OCaml does have +. for floats to make type checking easier, but Standard ML does not. Also, if Swift has operator overloading, why isn't it instantly clear that the RHS is an int, which can be assigned to a double?
This just looks like a performance bug in the type checker, and nothing that is inherent to HM.
People have been complaining about this issue for 10 years. Presumably if there were an easy fix they would have fixed it by now. They painted themselves into a corner somehow with HM, polymorphic literals and function overloading. Haskell doesn’t have function overloading (except for type classes) and OCaml doesn’t have polymorphic literals.
It seems like it’s not only function overloading (which, as you point out, Haskell does too by way of typeclasses) but also the implicit conversion between Int and Double. OCaml, Haskell, and Rust all require you to convert between them explicitly so they don’t need to figure out whether each 1 in the expression is an Int or a Double.
Am I seeing this correctly? Is HM + polymorphic literals + implicit type conversion the cause of Swift’s exploding compile time in such cases?
Ok, but then they should explain this particular case better. The RHS can be figured out just by choosing the overloaded operators.
In C++ terms, if you have int& operator+(const int&x, const int& y) then (1 + 1) is not ambiguous and can be selected fast. Same for unary minus etc.
The Swift devs should then blog about this example and explain step by step what is going on. If the literal "1" can be both an int and a float, that of course would be insane. Is that what you meant by "polymorphic literals"?
OCaml does have +. for floats to make type checking easier, but Standard ML does not. Also, if Swift has operator overloading, why isn't it instantly clear that the RHS is an int, which can be assigned to a double?
This just looks like a performance bug in the type checker, and nothing that is inherent to HM.