Re: Existential Type Declarations in Hugs

2001-05-03 Thread Mark Carroll 

On Thu, 3 May 2001 [EMAIL PROTECTED] wrote:
(snip)
> BTW, what is this "Skolem constant" that's referred to in the error message 
> that I received?

A combination of
http://www.sdsc.edu/~tbailey/teaching/cse151/lectures/chap09a.html and
http://cs.wwc.edu/~aabyan/Logic/normal.html may answer that for you. (-:

(It was too long ago now for me to remember much, and I'm not sure where
my notes are, so I daren't attempt an explanation myself!)

-- Mark


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Re: Existential Type Declarations in Hugs

2001-05-03 Thread Critterrathman 
In a message dated 5/3/2001 4:00:18 AM Central Daylight Time, 
[EMAIL PROTECTED] writes:

Should be:
    setx (MakeExistentialShape a) newx = MakeExistentialShape (setx a 
newx)
The result of setx must have the same type as its first argument.


Thanks.  That solves my problem.

BTW, what is this "Skolem constant" that's referred to in the error message 
that I received?

Chris Rathman

Re: Existential Type Declarations in Hugs

2001-05-03 Thread Marcin 'Qrczak' Kowalczyk 

Thu, 3 May 2001 02:54:26 EDT, [EMAIL PROTECTED] <[EMAIL PROTECTED]> pisze:

>class Shape a where
>   getx :: a -> Int
>   setx :: a -> Int -> a
> 
>data ExistentialShape =
>   forall a. Shape a => MakeExistentialShape a
> 
>instance Shape ExistentialShape where
>   getx (MakeExistentialShape a) = getx a
>   setx (MakeExistentialShape a) newx = setx a newx

Should be:
setx (MakeExistentialShape a) newx = MakeExistentialShape (setx a newx)
The result of setx must have the same type as its first argument.

-- 
 __("<  Marcin Kowalczyk * [EMAIL PROTECTED] http://qrczak.ids.net.pl/
 \__/
  ^^  SYGNATURA ZASTÊPCZA
QRCZAK


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