[Haskell-cafe] Type question in instance of a class

Jason Dagit dagit at codersbase.com
Sun Nov 16 17:31:47 EST 2008

On Sun, Nov 16, 2008 at 2:01 PM, Claude Heiland-Allen <
claudiusmaximus at goto10.org> wrote:

> I don't know how evil those language extensions are, though - I just
> fiddled until it worked...

The only part of FlexibleInstances that you've used here is the ability to
mention a type variable more than once in the instance.  I really wish this
came with MultiParamTypeClasses.  My reasoning is this, FlexibleInstances
turns on a lot of extra stuff, as do functional dependencies.  And yet, once
you have multiparam type classes one of the natural things you want is the
ability to mention a type variable more than once but currently you have to
enable a lot of extra baggage to get that ability.

I'm not an expert, the way you've used them together seems quite sane and by
using those extensions instead of some of the more powerful ones you've
probably done yourself a favor :)

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