On 06/09/10 11:23, Johannes Waldmann wrote:
We have overloaded numerical literals (Num.fromInteger) and we can overload string literals (IsString.fromString), so how about using list syntax ( [], : ) for anything list-like (e.g., Data.Sequence)?
I would have thought you have two obvious choices for the type-class (things like folding are irrelevant to overloading list literals): class IsList f where fromList :: [a] -> f a or: class IsList f where cons :: a -> f a -> f a empty :: f a I'd go for the first, as I'd imagine you are only overloading the [a,b,c] form, not the a:b:c:[] form, and the first reflects this better. Both of these could be used to convert a list literal into a list-like type (e.g. Sequence). But neither of them would be useful for sets or maps, because the classes lack an Ord constraint on the type a -- maybe this makes overloaded list literals fairly limited in utility. Thanks, Neil.