On Tuesday, March 4, 2014 11:34:55 AM UTC+5:30, Chris Angelico wrote: > On Tue, Mar 4, 2014 at 4:35 PM, Steven D'Aprano wrote: > > I have not used Haskell enough to tell you whether you can specify > > subtypes. I know that, at least for numeric (integer) types, venerable > > old Pascal allows you to define subtypes based on integer ranges, so I'd > > be surprised if you couldn't do the same thing in Haskell. > > The flexibility of the type system -- its ability to create subtypes and > > union types -- is independent of whether it is explicitly declared or > > uses type inference.
> I'm not sure how you could have type inference with subtypes. Short answer: You cant [Yeah Some folks dont like my short answers :-) ] Long answer: See the links I posted above Intermediate answer: Types (for a modern FPL) are like math sets except that: - set-membership is in general hard and in principle undecidable - type-membership had better be decidable and preferably linear-time if its to be part of an implementation (and not a philosophical discussion over a cuppa chai) - Which means that... > Static and dynamic typing both have their uses. But when I use static > typing, I want to specify the types myself. I'm aware that's a matter > of opinion, but I don't like the idea of the compiler rejecting code > based on inferred types. ...Type inference is strictly (aka mathematically) syntax even though in the implementation, the parsing phase and the type checking/inferencing phase are sequenced In short: An important flavor of the FP koolaid is the Damas-Milner type-inferencing algorithm. Damas-Milner + Subtyping is the recipe for a severe headache -- An important reason why FP and OOP are incompatible -- https://mail.python.org/mailman/listinfo/python-list
