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Irrefutable pattern exception when inserting edge from non-existent vertex #14

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robstewart57 opened this issue Jun 4, 2015 · 0 comments
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Irrefutable pattern exception when inserting edge from non-existent vertex #14

robstewart57 opened this issue Jun 4, 2015 · 0 comments

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@robstewart57
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Take the following example:

test :: Gr Int String
test = insEdge (0,1,"foo") (mkGraph [] [])

An evaluation attempt of test throws the following exception:

mkGraph *** Exception: Data/Graph/Inductive/Graph.hs:229:5-38: Irrefutable pattern failed for pattern (Just (pr, _, la, su), g')

The reason this is being thrown is because the vertex indexed with 0 does not exist in the graph I am trying to insert the edge into:

-- | Insert a 'LEdge' into the 'Graph'.
insEdge :: (DynGraph gr) => LEdge b -> gr a b -> gr a b
insEdge (v,w,l) g = (pr,v,la,(l,w):su) & g'
  where
    (Just (pr,_,la,su),g') = match v g

I'll send a pull request to add an informative error message in this case.
robstewart57 added a commit to robstewart57/fgl that referenced this issue Jun 4, 2015
@robstewart57
Informative error message for insEdge FIXES haskell#14
683255f 
As documented in haskell#14 , an
irrefutable pattern exception is thrown when attempting to insert an
edge from a vertex that does not exist in the graph, .e.g

    insEdge (0,1,"foo") (mkGraph [] [])

The previous behaviour of fgl was:

mkGraph *** Exception: Data/Graph/Inductive/Graph.hs:229:5-38: Irrefutable pattern failed for pattern (Just (pr, _, la, su), g')

The new behaviour is:

mkGraph *** Exception: insEdge: unable to add edge from non-existent vertex 0
@robstewart57 robstewart57 mentioned this issue Jun 4, 2015
Closed
robstewart57 added a commit to robstewart57/fgl that referenced this issue Jun 5, 2015
@robstewart57
Informative error message for insEdge
52ee0e8 
As documented in haskell#14 , an irrefutable pattern exception is
thrown when attempting to insert an edge from a vertex that does not
exist in the graph, .e.g

    insEdge (0,1,"foo") (mkGraph [] [])

The previous behaviour of fgl was:

mkGraph *** Exception: Data/Graph/Inductive/Graph.hs:229:5-38: Irrefutable pattern failed for pattern (Just (pr, _, la, su), g')

The new behaviour is:

mkGraph *** Exception: insEdge: unable to add edge from non-existent vertex 0

closes haskell#14
@robstewart57 robstewart57 mentioned this issue Jun 5, 2015
Closed
@ivan-m ivan-m closed this as completed in 7e9ffde Jul 13, 2015
psteiger pushed a commit to psteiger/fgl that referenced this issue Nov 8, 2015
@robstewart57 @psteiger
Informative error message for insEdge
48f9a28 
As documented in haskell#14 , an irrefutable pattern exception is
thrown when attempting to insert an edge from a vertex that does not
exist in the graph, .e.g

    insEdge (0,1,"foo") (mkGraph [] [])

The previous behaviour of fgl was:

mkGraph *** Exception: Data/Graph/Inductive/Graph.hs:229:5-38: Irrefutable pattern failed for pattern (Just (pr, _, la, su), g')

The new behaviour is:

mkGraph *** Exception: insEdge: unable to add edge from non-existent vertex 0

closes haskell#14
@ivan-m ivan-m mentioned this issue Oct 5, 2016
Closed
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Informative error message for insEdge robstewart57/fgl
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@robstewart57