parametric-polymorphism

What is the difference (if any) between these two F# type signatures? UseTheStream<'a when 'a :> Stream> : 'a -> unit and UseTheStream : (stream : Stream) -> unit Do they mean the same thing in this case? msdn says the following about the (:>) Type Constraint type-parameter :> type -- The provided type must be equal to or derived from the type specified, or, if the type is an interface, the provided type must implement the interface. This would indicate that the two signatures are saying the same thing. So Functionally, how are they different? Daniel They are different. Most importantly, the

Using the low-level GNU Science Library bindings Bindings.Gsl.RandomNumberGeneration , I'm running into this odd type behavior in GHCi where binding changes return type from a peek into GHC.Prim.Any . I'm trying to understand why since I can't use the c'rng_alloc unless I retain the type of pointer to an rng . For eample: λ> :t c'gsl_rng_alloc c'gsl_rng_alloc :: Ptr C'gsl_rng_type -> IO (Ptr C'gsl_rng) λ> :t p'gsl_rng_mt19937 p'gsl_rng_mt19937 :: Ptr (Ptr gsl_rng_type) λ> :t peek p'gsl_rng_mt19937 peek p'gsl_rng_mt19937 :: IO (Ptr gsl_rng_type) λ> x <- peek p'gsl_rng_mt19937 λ> :t x x :: Ptr

In the following Agda code, I have a term language based on de Bruijn indices. I can define substitution over terms in the usual de Bruijn indices way, using renaming to allow the substitution to proceed under a binder. module Temp where data Type : Set where unit : Type _⇾_ : Type → Type → Type -- A context is a snoc-list of types. data Cxt : Set where ε : Cxt _∷_ : Cxt → Type → Cxt -- Context membership. data _∈_ (τ : Type) : Cxt → Set where here : ∀ {Γ} → τ ∈ Γ ∷ τ there : ∀ {Γ τ′} → τ ∈ Γ → τ ∈ Γ ∷ τ′ infix 3 _∈_ data Term (Γ : Cxt) : Type → Set where var : ∀ {τ} → τ ∈ Γ → Term Γ τ 〈〉 :

I want to encapsulate a generic object in another class without setting the generic type argument. I created a base Animal<T> class and defined other subclasses from it. Example: public class Animal<T: YummyObject> { // Code } public class Dog: Animal<Bark> { // Code } public class Cat: Animal<Meow> { // Code } and defined an Animal property, without the type argument, in the UITableView extension bellow: extension UITableView { private static var animal: Animal! func addAnimal(animal: Animal) { UITableView.animal = animal } } but I get the following compile error when doing so: Reference to

Reading the paper on Types and Polymorphism in programming languages, i wondered is it possible to express the similar universal quantification on type members with Scala. Example from the paper: type GenericID = ∀A.A ↦ A Which is a type for generic identity function and the following example in their paper language Fun was correct: value inst = fun(f: ∀a.a ↦ a) (f[Int], f[Bool]) value intId = fst(inst(id)) // return a function Int ↦ Int Is there some way to express the similar thing in Scala? This is not the same as type constructor type GenericId[A] = A => A , cause it's a type operation

There are businesses and people. Users can either like or post a comment about a business but the same can not happen with a person. When a user posts something about a business or likes it, that business is called the target of that like or post: trait TargetingRelation[TargetingType[_],TargetedType] class Business class Person class Post[Target | TargetingRelation[Business,Post] ] { def target:Target } class Like[Target | TargetingRelation[Business,Like] ] { def target:Target } Here I'm inventing a T | P[T] notation meaning type parameter T such that it satisfies some property P[T] (or T :|: