Re: [Haskell-cafe] Fixing undeduceable instance ==> overlapping instance

24 Feb 2013


      On 02/24/2013 02:14 AM, Karl Voelker wrote:
...
On Sat, Feb 23, 2013 at 10:28 PM, Michael Orlitzky mailto:michael@orlitzky.com> wrote:
-- Recursive case, (n+2) x (n+2) matrices.
      instance (Eq a, Ring.C a, Arity n)
             => Determined (Mat (S (S n)) (S (S n))) a where
      determinant m =
        ...
        -- Recursive algorithm, the i,jth minor has dimension
        -- (n+1) x (n+1).
        foo bar (determinant (minor m i j))
I get an error stating that I'm missing an instance:
Could not deduce (Determined (Mat (S n) (S n)) a)
      ...
It looks to me like you just need to add (Determined (Mat (S n) (S n))
a) into the context of this instance. The problem is that the type
variable "n" could be almost anything (at least as far as this instance
definition knows).
So simple, thank you!