[Haskell-cafe] (automatic) type classes context inference
jpaulo at di.uminho.pt
Sat Aug 28 05:44:02 EDT 2010
I am developing a toolset in which I have several (multiparameter)
It is often the case that I can only define a data-type X as an
instance of one such class (say A), if X is an instance of another
class (say B);
The thing is that, while it is hard for me, because of all the type
parameters that I have to deal with, to add
'X is an instance of B'
to the context cxt_A in
'instance cxt_A => A X'
ghc is always able to correctly infer all type parameters; In fact, I
'Could not deduce (B X t1 ... tn)
from the context cxt_A arising from ...
Probable fix: add (B X t1 ... tn) to the context cxt_A ...'
In my case, this is the fix that I always need: most of the times, I
am just copy-pasting (B X t1 ... tn) to cxt_A!
Is there a way, say a compilation option, to avoid this?
can anyone please help me here? :)
thank you very much
João Paulo Fernandes
Universidade do Minho
More information about the Haskell-Cafe