[Haskell-cafe] Re: Graph library, was: Haskell.org GSoC

Benedikt Huber benjovi at gmx.net
Thu Feb 12 09:42:16 EST 2009

Daniel Kraft schrieb:
> Don Stewart wrote:
>>> - Graphs.
>> True graphs (the data structure) are still a weak point! There's no
>> canonical graph library for Haskell. 
> That sounds interesting...  What do you mean by "no canonical" library? 
>  Are there already ones but just no "standard" one?  But in this case, I 
> don't think adding yet another one will help :D  Or isn't there a "real" 
> general graph library?
I would also like to see a project working on a new graph library.
Currently, there is at least Data.Graph (just one Module, package 
containers), based on Array - adjacency lists, and the functional graph 
library (package fgl).

I think a good general purpose graph library is tricky though:
- There are lot of variants of graphs (trees, bipartite, acyclic, 
undirected, simple, edge labeled etc.), hard to find adequate and easy 
to use abstraction.
- There is no single 'best' implementation (mutable vs. unmutable etc.).
- Its hard to find good traversal and zipper abstractions, though fgl 
has some nice ones.
- The complexity of algorithms varies greatly depending on the 
particular kind of graph.
Anyway, that's why it is challenging and interesting.

> If so, this would be a nice thing to do :)  I could look at existing 
> ones (like Boost's graphs) to get a feeling for how an interface might 
> look like and what functionality to implement.
> BTW, is there some sort of "project hosting" specifically for such 
> Haskell projects?  Or should I go with sourceforge (for instance) for 
> developing this, if I gave it a try?
code.haskell.org / community.haskell.org
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