The [[dynamic rules]] mechanism can be used to enable a set of rules.

<verbatim>
  TriggerRules = 
	  ?Context(Bla, _);
		rules( A : ... -> ...	B : ... -> ... )

  traverse =
	  rec x({| A, B : try(TriggerRules + A + B); all(x) |})
</verbatim>
Rules =A= and =B= are only applied after a =Context(Bla,...)= has been encountered.

This is not always appropriate. Often the applicability of rules can be determined by the position in
the tree.

-- Main.EelcoVisser & Lennart Swart - 22 May 2002 <br />