[GHC] #2068: need better exception names for fgl

[GHC]

#2068: need better exception names for fgl
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    Reporter:  Frederik         |       Owner:                   
        Type:  feature request  |      Status:  new              
    Priority:  normal           |   Component:  libraries (other)
     Version:  6.8.2            |    Severity:  normal           
    Keywords:                   |    Testcase:                   
Architecture:  Unknown          |          Os:  Unknown          
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 Every once in a while, due to bugs in my code, when using fgl I see
 exceptions such as "Edge Exception, Node: 30". I think it would be better
 if messages like this in the library could be more informative, such as
 "Invalid node 439 in edge from node 30" or "Duplicate node 30" etc. Given
 that there is a problem with the graph, and given that graphs are made of
 nodes and edges, it is a good bet that the problem has something to do
 with a node or an edge, so saying "Node Exception" or "Edge Exception"
 doesn't provide users with very much information.

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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2068>
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