@@ -199,7 +199,7 @@ patchThatChangesMap oldByIndex newByIndex = patch
199 putRemainingKeys $ Set.delete k fromKs
199 putRemainingKeys $ Set.delete k fromKs
200 return $ NodeInfo (From_Move k) $ Just undefined -- There's an existing value, and it's here, so no patch necessary
200 return $ NodeInfo (From_Move k) $ Just undefined -- There's an existing value, and it's here, so no patch necessary
202− (fromK, remainingKeys) <- return . fromJust $ Set.minView fromKs -- There's an existing value, but it's not here; move it here
202+ (fromK, remainingKeys) <- return . fromMaybe (error "patchThatChangesMap: impossible: fromKs was empty") $ Set.minView fromKs -- There's an existing value, but it's not here; move it here
203 putRemainingKeys remainingKeys
203 putRemainingKeys remainingKeys
204 return $ NodeInfo (From_Move fromK) $ Just undefined
204 return $ NodeInfo (From_Move fromK) $ Just undefined
205 Map.traverseWithKey f newByIndex
205 Map.traverseWithKey f newByIndex