On Fri, 2 Apr 2004, Christian Maeder wrote:
How many implemenations to you want? Eventually I suspect about 3 implemenations to be useful.
Dessy currently has (and none of them is useless): Streams (the only possible lazy implementation) Real-time Queues Deques Write-only Sequences (like the OrdList) Democratic Sequences (the default)
I don't know if the size of a class matters, but some code duplication could be avoided by a minimal class (empty, isEmpty, cons, head, tail) as well.
With these primitives you would just mimick the concrete [] data type, making efficient implementations of almost all other functions impossible. As I argue in http://www.stud.tu-ilmenau.de/~robertw/dessy/fun/democratic/ a "core" consisting of (concat front back) efficiently implemented (i.e. logN each) will permit every other function to be implemented in O(logN). However, most implementations will also provide constant-time (is_empty size first last), and some implementations will also provide constant-time (add_first add_last but_first but_last). Furthermore we need of course 'fold', but also many implementations can implement (apply filter) faster (albeit only by a constant factor) than the default implementation: apply f = fold empty (single . f) (<+>) filter p = fold empty (\x -> if p x then single x else empty) (<+>) Thus, a minimal class will not be small. But I already explained last time, that this is really no problem. Robert