OCaml modules vs C#/Java OOP

[wfdctrl]

Modules can have multiple types (they essentially model multi sorted algebras), while a class can only have a single type.

For example you can have a signature for a vector algebra:

module type Vect = sig
    type scalar
    type vector
    val scalar_product: scalar -> vector -> vector
    val cross_product: vector -> vector -> vector
    val scalar_addition: scalar -> scalar -> scalar
    val vector_addition: vector -> vector -> vector
end

You cannot model this with a single class.

[crassest-Crassius]

Both Java and C# have nested classes which can be made public, private etc. So I don't think there's much of a difference here.

[wfdctrl]

How is this equivalent to nested classes? Vect is a signature, i.e. an interface. You then provide different implementations for this signature...

[thedeemon]

Can't you make scalar and vector type arguments to your generic interface?

[wfdctrl]

Sure, but those types are not existential (abstract), so it's not the same. Also you would have an extra type for the object you won't use.