Modify transform so it can create an exception

Libraries/iTasks/WF/Combinators/Core.dcl

@@ -4,6 +4,7 @@ definition module iTasks.WF.Combinators.Core
 */
 import iTasks.WF.Definition
 from iTasks.SDS.Definition import :: SDS
+from Data.Error import :: MaybeError(Ok)
 from Data.Maybe import :: Maybe
 
 //* Next task actions
@@ -78,16 +79,29 @@ ActionClose		:==	Action "Close"
 
 derive class iTask AttachException
 instance toString AttachException
+
+/**
+* Adds a result transformation function to a task.
+* The resulting task is still considered a single step in the workflow.
+*
+* @param Function: The transformation function.
+* @param Task: The task to which the transformation function is added
+*
+* @return The transformed task
+*/
+transformError :: ((TaskValue a) -> MaybeError TaskException (TaskValue b)) !(Task a) -> Task b
+
 /**
 * Adds a result transformation function to a task.
 * The resulting task is still considered a single step in the workflow.
 *
-* @param Function: The transformation function. It works on maybe's to also map over instable tasks.
+* @param Function: The transformation function.
 * @param Task: The task to which the transformation function is added
 *
 * @return The transformed task
+* @type ((TaskValue a) -> TaskValue b) !(Task a) -> Task b
 */
-transform :: ((TaskValue a) -> TaskValue b) !(Task a) -> Task b
+transform f :== transformError (\tv->Ok (f tv))
 
 /**
 * The generic sequential combinator.

Libraries/iTasks/WF/Combinators/Core.icl

@@ -72,12 +72,13 @@ where
 
 derive class iTask AttachException
 
-transform :: ((TaskValue a) -> TaskValue b) !(Task a) -> Task b
-transform f (Task evala) = Task eval
+transformError :: ((TaskValue a) -> MaybeError TaskException (TaskValue b)) !(Task a) -> Task b
+transformError f (Task evala) = Task eval
 where
 	eval event evalOpts tree iworld = case evala event evalOpts tree iworld of
-		//TODO: guarantee stability
-		(ValueResult val lastEvent rep tree,iworld)	= (ValueResult (f val) lastEvent rep tree, iworld)
+		(ValueResult val lastEvent rep tree,iworld)	= case f val of
+			Error e = (ExceptionResult e, iworld)
+			Ok v = (ValueResult v lastEvent rep tree, iworld)
 		(ExceptionResult e, iworld)				    = (ExceptionResult e, iworld)
 		(DestroyedResult, iworld)					= (DestroyedResult, iworld)