21 Sep
2009
21 Sep
'09
2:19 a.m.
On Sun, Sep 20, 2009 at 06:43:53PM -0700, Alexander Solla wrote:
data Add a b = Add a b instance ( Evaluate a , Evaluate b ) => Evaluate (Add a b) where
Okay.
data Value (Sum a b) = SumValue (Sum a b)
Hmmm, have you tried
data Value (Add a b) = AddValue (Value a) (Value b)
Now your 'value' function would be
value (AddValue va vb) = value va + value vb
because you're holding 'Value a' and 'Value b', not 'a' and 'b'. It may help to think as if this class represented a container. For value, do you need the whole container or just one of its elements? I know other will give a better explanation, but maybe this is enough to get you in the right track :). HTH, -- Felipe.