[Haskell-cafe] Re: Approaches to dependent types (DT)

[Benjamin Franksen]

pbrowne wrote:
> Dependent Types (DT)
> The purpose of dependent types (DT) is to allow programmers to specify
> dependencies between the parameters of a multiple parameter class.  

'Dependent type' means result type (of a function) can depend on argument 
values. This is not (directly) supported in Haskell.

What you are talking about is called 'functional dependencies', not 
'dependent types'. Sometimes abbreviated as 'fundeps'.

> DTs
> can be seen as a move towards more general purpose parametric type
> classes. 

This is at least misleading, as adding a functional dependency does not make 
the class more general, but more special, as it reduces the number of 
possible instances.

Cheers
Ben