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

Benjamin Franksen ben.franksen at online.de
Mon Jan 11 07:55:01 EST 2010

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.


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