How about this? Don't say Santa never comes:
Foo.hs:5:
Ambiguous type variable(s) `a' in the constraint `Eq a'
arising from use of `==' at Foo.hs:5
In the first argument of `&&', namely `(b == b)'
In a guard for an equation for `example': (b == b) && (a == a)
> -----Original Message-----
> From: Marc van Dongen
> Sent: Monday, September 13, 1999 5:53 PM
> To: [EMAIL PROTECTED]
> Subject: Dear Santa (Error Messages)
>
>
> Dear GHC-Santas,
>
>
>
> I also have a wish list and one of the things I would
> like to aks for is a change in error messages generated
> by ghc(-4.04 in this case). In my opinion this would
> make it easier to locate the cause of an error.
>
> I shall use a contrived code example to illustrate
> what I mean:
>
> > module Example( example ) where
>
> > example :: Eq a => a -> a
> > example a
> > | (b == b) && (a == a) = a
> > where b = error []
>
> Example.lhs:5:
> Ambiguous type variable(s) `a'
> in the constraint `Eq a'
> arising from use of `==' at Example.lhs:5
>
> I think this message could be improved by adding some more
> information:
> 1) Mention the name(s) of the variable(s) with type `a'
> which caused the error (There are two variables
> used in line 5 and the use of only one of them causes
> the error);
> 2) Mention which instance of `==' in line 5 caused
> the error (There are two such things in line 5
> each with a constraint of the form `Eq a.' One
> only causes the error).
>
> It is my experience that as code fragments become larger
> (and constraints are very loose,) the search space for
> potential errors gets large at a very rapid speed. Any
> additional information to prune this search space will
> make the problem of locating actual errors signifficantly
> more easy.
>
> Please note that this is not at all the highest point on
> my wish list. I only mention it because I think it would
> improve using ghc. In other words: Feel free to ignore.
>
>
> Regards,
>
>
> Marc van Dongen
> _______________________________________________________
> Marc van Dongen, CS Dept | phone: +353 21 903578
> University College Cork, NUIC | Fax: +353 21 903113
> College Road, Cork, Ireland | Email: [EMAIL PROTECTED]
>
