Merge pull request #152 from Haskell-Things/more_debugging

add more debugging messages in failure cases.

Graphics/Slicer/Math/Skeleton/Definitions.hs

@@ -414,7 +414,7 @@ ancestorsOf :: INodeSet -> [INodeSet]
 ancestorsOf (INodeSet children _)
   | isEmpty children = []
   | otherwise = case SL.last children of
-                  [] -> error "encountered an empty generation."
+                  [] -> [] -- error $ "encountered an empty generation: \n" <> show children <> "\n"
                   [a] -> [INodeSet (SL.init children) a]
                   newParents -> case SL.init children of
                                   (Slist [] 0) -> INodeSet mempty <$> newParents

Graphics/Slicer/Math/Skeleton/Face.hs

@@ -216,11 +216,11 @@ getFaces' origINodeSet eNodeSet iNodeSet iNode = findFacesRecurse iNode myPLines
          | isENode eNodeSet (fst pLine)                              = [] -- don't climb down an enode, you're done
          | hasArc myINode && isCollinear (outAndErrOf myINode) pLine = [] -- don't try to climb back up the tree
          | isNothing iNodeSet = error "we need INodes here."
-         | ancestorsOf (fromJust iNodeSet) /= [] = myGetFaces $ onlyOne $ filter (\a -> outAndErrOf (finalINodeOf a) == pLine) $ ancestorsOf (fromJust iNodeSet)
+         | not $ null (ancestorsOf $ fromJust iNodeSet) = myGetFaces $ onlyOne $ filter (\a -> outAndErrOf (finalINodeOf a) == pLine) $ ancestorsOf (fromJust iNodeSet)
          | otherwise = error "no between to plant?"
           where
             onlyOne :: (Show a) => [a] -> a
-            onlyOne [] = error "no item"
+            onlyOne [] = error $ "no item!\n" <> show pLine <> "\n" <> show iNodeSet <> "\n"
             onlyOne [a] = a
             onlyOne xs = error $ "too many items." <> show xs <> "\n"
             myGetFaces newINodeSet