2008/6/12 Stephan Friedrichs
For "index", don't use Monad, use Maybe (I think that's what the recent libraries@haskell.org discussion concluded, in the context of switching Data.Map back to Maybe).
I was just copying the idea from Data.Map and it's usually a good thing to have functions as general as possible, or why is it not?
Mainly because it's too easy to use them in a Monad that does not have a meaningful fail(), like IO, many beginners do this error and are surprised when their program is less robust that it should be. On the other hand it's pretty easy to get an error out of a Maybe (for example you can use fromMaybe with error() to get a meaningful error output).
Also, Data.List has genericLength etc, to
At the moment, I'm using the Int type for size and indexing only for one reason: I haven't found a proper way to generalize it. I'd really like to use the Ix class, but it doesn't provide enough functionality, it only works on fixed-size intervals (i. e. for arrays, which don't change their size, but a list does). Maybe someone has an idea of how to realize lists with a variable starting index and size?
Given that this structure isn't lazy enough, I really don't see a problem with using Int (any random access list with a size that needs an Integer would blow the memory anyway...). -- Jedaï