lastTail (ZLast l) = l
lastTail (ZTail _ t) = lastTail t
-tailOfLast l = ZLast (LastOther l) -- ^ tedious to write in every client
+tailOfLast l = ZLast (LastOther l) -- tedious to write in every client
------------------ simple graph manipulations
lift (Nothing, _) = Nothing
lift (Just b, bs) = Just (b, bs)
--- | 'insertBlock' should not be used to *replace* an existing block
+-- | 'insertBlock' should not be used to /replace/ an existing block
-- but only to insert a new one
insertBlock :: Block m l -> BlockEnv (Block m l) -> BlockEnv (Block m l)
insertBlock b bs =
-- more mathematically elegant (but results in more complicated code).
--
-- Here's an easy way to go wrong! Consider
+-- @
-- A -> [B,C]
-- B -> D
-- C -> D
+-- @
-- Then ordinary dfs would give [A,B,D,C] which has a back ref from C to D.
-- Better to geot [A,B,C,D]