On 29 October 2010 23:28, Uwe Schmidt
Dear Haskellers,
I've a question about type class design. When developing the set of functions for a class, there are often two or more functions, let's say f and g, where the semantics of g can be expressed by f.
When writing down the code, there are two choices for g. First g is included in the type class, second g is defined outside and the signature has a context referencing the class.
1. case
class Foo a where f :: ... a ... g :: ... a ... g = expr[f]
2. case
class Foo a where f :: ... a ...
g :: Foo a => ... a ... g = expr[f]
[snip]
My argument for 2.:
c) Correctness: The semantics for g are fix (relative to f), All laws for g hold everywhere, assuming f is implemented correctly.
Another possible argument: large type classes can look daunting for both implementors and users, even if only one or two methods need to be defined for a minimal instantiation (I'm tring to work out what to do here myself, as I have some typeclasses that for efficiency reasons it might be nice to have more methods in the class, but it makes it a little overwhelming). -- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com