[Haskell] To all users of FGL

[Ivan Lazar Miljenovic]

As you may now, for the past few months I've been (finally!) cleaning
up FGL, adding tests, etc.

One of the issues that has arisen with this is that the behaviour of
the delLEdge [1] function is not well specified when dealing with
multiple edges.

Specifically, the documentation states that the purpose is to "Remove
*an* LEdge from the Graph." (emphasis added)... but the behaviour when
dealing with multiple edges is to remove *all* such edges from the
graph.

The current version on GitHub is to instead just delete a single such
labelled edge, with a new function "delAllLEdge" that replicates the
current behaviour.

Before releasing this change, however, I wanted to make sure that I
wouldn't break people's code if they rely upon this functionality; I
did try and search through GitHub to see who - if anyone - is using
this function, but primarily found various copies of fgl embedded into
other people's repositories.

As such, please check your code and let me know if this change in
behaviour might affect you (if this is the case, I might let delLEdge
keep the current behaviour and have a new function delete just one
edge).

[1]: http://hackage.haskell.org/package/fgl-5.5.1.0/docs/Data-Graph-Inductive-Graph.html#v:delLEdge

-- 
Ivan Lazar Miljenovic
Ivan.Miljenovic at gmail.com
http://IvanMiljenovic.wordpress.com