On Oct 21, 2010, at 9:58 PM, Simon Peyton-Jones wrote:
So GHC's behaviour is probably about right, but the description is wrong.
On Oct 21, 2010, at 11:14 PM, Sebastian Fischer wrote:
An implicit quantification point is a) the type in a type signature f :: type or b) a type of the form (context => type) if it does not start with an explicit 'forall'
I have mixed feelings about b). A special treatment of contexts is convenient but also confusing because they are treated differently depending on where they occur. It is convenient because one can omit 'forall's in higher-rank types if they use contexts. It is confusing because types with context in type signatures are treated differently than types with context in data declarations (because type signatures are implicit quantification points and arguments in data declarations are not.) How inconvenient would it be to make the above description simpler by dropping b) and thus require more explicit 'forall's? I don't know what I prefer. I like both convenience and simplicity of explanations and cannot judge wich alternative has more convincing arguments in this case. Sebastian