Re: [Haskell-beginners] Question about constraints, signatures

9 May 2011

      On 2011-05-09, at 4:04 AM, David Virebayre wrote:
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2011/5/8 Philippe Sismondi :
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On 2011-05-06, at 12:12 PM, Brent Yorgey wrote:
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On Fri, May 06, 2011 at 11:34:47AM -0400, Philippe Sismondi wrote:
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I am trying to understand the Typeclassopedia article by Brent Yorgey in Monad.Reader. I am simultaneously working my way through Real World Haskell, so I may be doing things a bit out of order.
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I (more or less) understand that types and typeclasses are not the same.
But it seems to me that they do conflate in a way, if we think of types as defined by functions on them.
So why should we not be able to write:
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f ::  Num d -> String -> Int
You can have multiple class constraints, so it's not clear how you
would write them using your syntax; how would you write :
f :: (Eq d, Ord d) => d -> String -> Int ?
Also, you only have to tell the class constraint once, with your syntax
g :: (Num d) => d -> d -> d
would become:
g :: Num d -> Num d -> Num d
but that syntax lets you write nonsense :
h :: Num d -> Eq d -> Ord d
David.
David:

Thanks for your input. As I have quite a distance to go with Haskell, I shall take all these comments under advisement.

- Phil -