[moving to libraries] On Tue, Jan 13, 2004 at 05:46:29PM +0100, Wolfgang Jeltsch wrote:
for my studies I recently needed graph and tree handling code. Because nothing I found seemed to satisfy my needs, I finally started writing my own graph and tree module. I was especially disappointed with Data.Graph and Data.Tree. The reasons are: * The Implementation of the types is not hidden so that code using Data.Graph and Data.Tree can get very implementation-dependent. * Vertices are ints which is too low level in my opintion. I think it would be better to allow different types for vertices because this seems to closer reflect what applications demand. * I'd prefer to be able to use arbitrary sets of vertices instead of only continuous ranges. * There are only very few functions for trees and forests.
The Data.Tree module in base is certainly quite small. You've made two changes: * made the types abstract, but provided the equivalent constructor and destructor functions. I'm not sure that gains anything. * added upwards and downwards accumulators (except that your "upwards" accumulator is actually a variant downwards accumulator, with quadratic performance). It might be worthwhile to add fold and accumulators. I was also thinking of adding unfolds (pure, and monadic depth-first and breadth-first).