The =bound-unbound-vars= component of the [[Stratego optimizer]] annotates variables with one of the annotations 
="bound"=, ="unbound"=, or ="(un)bound"=, with the following meanings:

	* ="bound=" : the variable has been bound in a previous match
	* ="unbound=" : the variable has been declared in a scope, but is not yet bound in a match
	* ="(un)bound"= : the variable may or may not be bound
 
Variables are bound in matches, used in builds, and refreshed in scopes. 
Choice operators may lead to a variable being bound in one path, but not in the
other. Such variables are annotated with "(un)bound".

This analysis is used in the [[StrategoFrontEnd]] for [[use def analysis]], in the optimizer for [[dead variable elimination]],
and in the back-end to [[avoid run time checks on variables]].

-- Main.EelcoVisser - 17 Aug 2003