HALFEDGE: improve readability

Graphics/HalfEdge.hs

@@ -166,24 +166,26 @@ indirectToDirect :: [a]                       -- ^ list of points
                  -> [IndirectHeFace]
                  -> Map.IntMap IndirectHeVert -- ^ assumed to start at index 1
                  -> HeEdge a
-indirectToDirect pts pe@(e:_) fs vertarr
+indirectToDirect pts pe@(e:_) fs vertmap
   = thisEdge e
   where
     thisEdge (IndirectHeEdge ei sv _ fi off)
-      = case (fs `atMay` fi, pe `atMay` (ei + off), Map.lookup sv vertarr) of
+      = case (fs `atMay` fi, pe `atMay` (ei + off), Map.lookup sv vertmap) of
-          (Just x, Just y, Just z) -> HeEdge (thisVert z sv)
+          (Just face,
+           Just edge,
+           Just vert) -> HeEdge (thisVert vert sv)
                                 (getOppEdge sv fi)
-                                             (thisFace x)
+                                (thisFace face)
-                                             (thisEdge y)
+                                (thisEdge edge)
           _           -> NoEdge
     thisFace (IndirectHeFace (_, vi:_))
       = case pe `atMay` vi of
-          Just x  -> HeFace (thisEdge x)
+          Just edge -> HeFace (thisEdge edge)
           Nothing   -> NoFace
     thisFace (IndirectHeFace _) = NoFace
     thisVert (IndirectHeVert eedg _) coordi
       = case (pts `atMay` (coordi - 1), pe `atMay` (eedg - 1)) of
-          (Just x, Just y) -> HeVert x (thisEdge y)
+          (Just vert, Just edge) -> HeVert vert $ thisEdge edge
           _                      -> NoVert
     getOppEdge sv fi
       = case join
@@ -192,8 +194,8 @@ indirectToDirect pts pe@(e:_) fs vertarr
                . catMaybes
                . fmap (pe `atMay`)
                . edgelist
-               <$> Map.lookup sv vertarr of
+               <$> Map.lookup sv vertmap
-        Just x  -> thisEdge x
+        of Just x  -> thisEdge x
            Nothing -> NoEdge
 indirectToDirect _ _ _ _ = NoEdge