TRACE activity

Often users would like to be able to view temporary results in Thor. The only real way of doing that at the moment is to add an output statement. However that has some drawbacks

• inefficient they may only be interested in the first few rows.
• It doesn't work very well for child queries.
• Adding the output modifies the structure of the graphs being generated.

It would be good to come up with a step towards a thor debugger which made this easier for the users.

• E.g., a pseudo-activity which could be used to indicate a certain number of records should be kept so they can be displayed.

tracedX := TRACE(x, KEEP(100));

Should we also have the ability to select a link in a graph and indicate that values should be kept for that link?

(May or may not be related to the option to force a graph spill at a particular point.)