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.

-- EelcoVisser - 17 Aug 2003