Stronger static types, was Re: [Haskell-cafe] Re: Versioning

[Lennart Augustsson]

It's possible to augment Haskell type system to be the one in  
Epigram.  But it would no longer be Haskell. :)  And to meet the  
goals of Epigram you'd also have to remove (unrestricted) recursion  
from Haskell.

	-- Lennart

On Dec 21, 2006, at 23:46 , Brian Hulley wrote:

> Jacques Carette wrote:
>> Yes, dependent types have a lot to do with all this.  And I am an
>> eager lurker of all this Epigram.
>
> Would it be possible to augment Haskell's type system so that it  
> was the same as that used in Epigram?
> Epigram itself uses a novel 2d layout and a novel way of writing  
> programs (by creating a proof interactively) but these seem  
> orthogonal to the actual type system itself.
>
> Also, typing is not the only issue for compile time guarantees.  
> Consider:
>
>    data Dir = Left | Right | Up | Down deriving Eq
>
>    -- Compiler can check the function is total
>    foo :: Dir -> String
>    foo Left = "Horizontal"
>    foo Right = "Horizontal"
>    foo Up = "Vertical"
>    foo Down = "Vertical"
>
> versus
>
>    -- Less verbose but compiler can't look inside guards
>    foo x | x == Left || x == Right = "Horizontal"
>    foo x | x == Up || x == Down = "Vertical"
>
> versus something like:
>
>    foo (Left || Right) = ...
>    foo (Up || Down) = ...
>
> Brian.
> -- 
> http://www.metamilk.com
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