Re: [Haskell-cafe] Flexible instances

[Albert Y. C. Lai]

George Pollard wrote:

I'm a little confused. Why is this allowed:

instance Eq Blah where
        x == y = True

But not this:

Illegal instance declaration for `Stringable [Char]'
        (All instance types must be of the form (T a1 ... an)
         where a1 ... an are distinct type *variables*
         Use -XFlexibleInstances if you want to disable this.)
    In the instance declaration for `Stringable [Char]'

'Blah' isn't a type variable, is it? Is my brain just not working right
today?

Just in case: n=0 for "instance Eq Blah", i.e., "T a1 ... an" becomes "T".
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