hunk ./src/Data/EventList/Relative/TimeBody.hs 42
+    toAbsoluteEventListGen, fromAbsoluteEventListGen,
hunk ./src/Data/EventList/Relative/TimeBody.hs 542
-toAbsoluteEventList start =
-   AbsoluteEventPriv.Cons . decons .
-   flip evalState start .
-   mapTimeM (\dur -> modify (dur+) >> get)
+toAbsoluteEventList = toAbsoluteEventListGen (+)
hunk ./src/Data/EventList/Relative/TimeBody.hs 546
-fromAbsoluteEventList =
-   flip evalState 0 .
+fromAbsoluteEventList = fromAbsoluteEventListGen (-) 0
+
+{- |
+Convert from relative time stamps to absolute time stamps
+using a custom accumulator function (like @(+)@).
+-}
+toAbsoluteEventListGen ::
+   (absTime -> relTime -> absTime) ->
+   absTime -> T relTime body -> AbsoluteEventList.T absTime body
+toAbsoluteEventListGen accum start =
+   AbsoluteEventPriv.Cons . decons .
+   flip evalState start .
+   mapTimeM (\dur -> modify (flip accum dur) >> get)
+
+{- |
+Convert from absolute time stamps to relative time stamps
+using custom subtraction (like @(-)@) and zero.
+-}
+fromAbsoluteEventListGen ::
+   (absTime -> absTime -> relTime) ->
+   absTime ->
+   AbsoluteEventList.T absTime body -> T relTime body
+fromAbsoluteEventListGen diff start =
+   flip evalState start .
hunk ./src/Data/EventList/Relative/TimeBody.hs 571
-      (\time -> do lastTime <- get; put time; return (time-lastTime)) .
+      (\time -> do lastTime <- get; put time; return (diff time lastTime)) .