[Haskell-cafe] Re: What makes Haskell difficult as .NET?

[Maciej Piechotka]

On Fri, 2010-05-14 at 22:54 -0400, C. McCann wrote:
> On Fri, May 14, 2010 at 8:39 PM, Maciej Piechotka <uzytkownik2 at gmail.com> wrote:
> > 1. Haskell Class/Type famillies/... are conceptually different then
> > classes and interfaces.
> 
> I believe interfaces would be roughly equivalent to the subset of
> single-parameter type classes such that:
>   - All type class methods are functions
>   - The first argument of each function is the class's type parameter,
> fully applied to any type parameters it needs
>   - The class's type parameter appears nowhere else
> 

I'm not sure but also:

- you can write always a new class in Haskell:

class Abc x where
	abc :: x -> Int

instance Abc Int where abc = id

IIRC .Net interfaces cannot be added outside assembly (I may be wrong).
On the other hand Haskell does not have inheritance.

Generally
	Haskell: newtype/data specify data (and type) while classes provides
basic abstract operations on it.
	C#/Java/...: Classes specify data AND how to operate on it (including
non-basic operators) and interfaces abstract operations.

- It is not that it can occur once:

class Abc x where
	abc :: x -> [x]

is roughly:

interface Abc<in T> {
	public IList<T> abc();
}

- It seems that it is not possible to have default implementations in
interfaces.

> > 2. As .Net does not differentiate between IO a and a Haskell cannot feel
> > completely native (hand-made FFI or everything in IO)
> 
> Wouldn't be any worse than using most C bindings in Haskell as is. Or
> using a lot of .NET libraries in F#, to be honest, if you try to write
> functional-idiomatic instead of quasi-imperative code.
> 
> Though, considering the near-omnipresent possibility of null
> references, most .NET functions would actually need to return
> something of the form "IO (Maybe a)".
> 

However the problem is that the .Net is suppose to be a single platform
with different syntaxes attacked to it. It does not stop to use F#
operations (without syntax sugar) in C# or VB.

Haskell on .Net would be a foreigner as it is on C. 

Regards
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