The typechecker doesn’t know when to apply the subsumption rule. You can tell it when with the following function. Prelude> let u :: ((f a -> f a) -> c) -> ((forall b. f b -> f b) -> c); u f n = f n This says, given a function from a transformation for … Read more
There’s no fundamental limitation of .NET that stops functors from being implemented in F#. True, they can’t be represented directly in .NET metadata, but neither can other F# language features like union types. Compilers for languages with functors (e.g., Standard ML, OCaml) have a pass called defunctorize; it works just like C++ template expansion, in … Read more
My usage can be divided into the following 5 categories. 1. interface 2. modularity 3. legibility 4. brevity 5. tricks If the variant type is only internal to the module, I use regular variants, because as you said they are compiled more efficiently. If the variant type is exported in the interface and I feel … Read more
There are some differences feature-wise, as well as semantically. Features SML supports but not OCaml: transparent signature ascription module-level let symmetric sharing constraints syntactic sugar for functors over types and values Features OCaml 4 has but not SML: higher-order functors recursive modules local modules nested signatures modules as first-class values general module sharing (sig with … Read more
The main place to do the comparison is, ML Modules and Haskell Type Classes: A Constructive Comparison. Stefan Wehr and Manuel M.T. Chakravarty. In Proceedings of The Sixth ASIAN Symposium on Programming Languages and Systems – APLAS 2008, Springer-Verlag, LNCS, 2008. Modular Type Classes. Derek Dreyer, Robert Harper, and Manuel M. T. Chakravarty. In Proceedings … Read more
There are lots of differences, some technical, some sociopolitical. I’ve tried to put more important differences first. SML is a language with a definition and a standard. It is stable (and in fact has been frozen so it cannot evolve). Objective Caml is an implementation controlled by a small group at INRIA. It continues to … Read more