On 01/07/10 12:37, Patrick Browne wrote:
Why do some cases such as 1) fail to run even if they are the only instantiation.
-- 1) Compiles but does not run instance LocatedAt Int String where spatialLocation(1)="home"
That instance is fine. I presume the problem is that you are trying to run this function using "spatialLocation 1" as the function call. The problem with that is that the "1" part has type Num a => a, i.e. it can be any Num type. Even though you only have one instance, that's not used to constrain the type for "1". The call "spatialLocation (1::Int)" works correctly. Looking at your other examples, all the ones that don't work have a numeric type for the parameter, so I suspect it is the same issue throughout. Thanks, Neil.