2007/9/2, Peter Verswyvelen
Can the same be done on other builtin constructs? For example, if I have [a], can this list be lifted to other types? I guess not, because no type class exists for the list type?
You can indeed already do that, except it won't be a single instance since list have a bucketful of interesting properties. A good starting is looking at what list is an instance of and trying to identify the set of instance which interest us in this case, Foldable and Functor are probably a good start, embodying most of the interesting way to access a data structure as a list (head and tail don't really make sense for most of the alternatives, except other "sequence" library which currently provide this functionality in an ad-hoc way, see Sequence and ByteString for example of that). An alternative is Traversable. -- Jedaï