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(guile.info)Guardians

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Guardians
=========

 - primitive: make-guardian
     Create a new guardian.  A guardian protects a set of objects from
     garbage collection, allowing a program to apply cleanup or other
     actions.

     make-guardian returns a procedure representing the guardian.
     Calling the guardian procedure with an argument adds the argument
     to the guardian's set of protected objects.  Calling the guardian
     procedure without an argument returns one of the protected objects
     which are ready for garbage collection or `#f' if no such object
     is available.  Objects which are returned in this way are removed
     from the guardian.

     See R. Kent Dybvig, Carl Bruggeman, and David Eby (1993)
     "Guardians in a Generation-Based Garbage Collector".  ACM SIGPLAN
     Conference on Programming Language Design and Implementation, June
     1993.