[Haskell-beginners] A few really short beginners questions

[Daniel Fischer]

On Monday 04 October 2010 15:44:53, Brent Yorgey wrote:
> On Sun, Oct 03, 2010 at 09:44:28PM +0200, Klaus Gy wrote:
> > Yea, Hugs tells me:
> >
> > ERROR (filepath):3 - Syntax error in instance head (constructor
> > expected)
> >
> > But since I'm trying to understand Haskell and have nothing particular
> > in mind with this program, I'm not stressed finding a solution for
> > this. I'm happy if the code is principally correct.
>
> Ah, I see, you are using Hugs.  As I mention in my other email, GHC
> has an extension (FlexibleInstances) to allow this.  Hugs might
> support this extension as well (I am not sure)

It does, but AFAIK, hugs offers less fine-grained control over which 
extensions to enable, you need the -98 command line option, which turns on 
almost all extensions hugs has (I think the only extension individually 
controllable is overlapping instances, +o or +O for unsafe overlapping 
instances).

> but it unfortunately
> doesn't mention the possibility in the error message, like GHC does.
>
> -Brent