*CATCH vs named PROG

[Robert W. Kerns <RWK at MIT-MC>]

*CATCH is not the same.  For one thing, it's dynamicly scoped, not
lexical.  This is not the semantics we're looking for.  Why not flush
RETURN and always use *CATCH/*THROW instead?  This means it must
compile to something a couple orders of magnitude slower than the
pop/jump sequence of a named prog and return.  *THROWs outside the
context where they should be allowed would find the *CATCH above them,
unlike the construct we're looking for.