[R6RS] Unbound variables

[Michael Sperber]

This is referring to Will's classification of exceptional situations
that he just committed to the respository:

4.1.1   reference to unbound variable  error       should &undefined
5.2.1   set! (unbound variable)        error       should &undefined (!!!!!)
5.2.1   set! (w/o defining)            unspecified should &undefined (!!!!!)

At least within a library module, I vote for turning these "should"s
into "must"s.

-- 
Cheers =8-} Mike
Friede, Völkerverständigung und überhaupt blabla