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Using EQ instead of EQL to compare catch tags
From: Masinter.pa at XEROX.ARPA
To: COMMON-LISP at SU-AI.ARPA
It seems clear that the "portable subset" of Common Lisp has to either
insist that EQL be used for catch-tags, or else refuse to allow anything
other than a symbol.
That makes very little sense to me. Non-symbol, non-numeric catch tags are
useful. For example, to correctly implement the contorted example on page 40,
one must create a unique catch tag at runtime (that's done quickly and portably
with CONS). The only place I can imagine numeric catch tags being used is in
code generated by the compiler or some program-writing-program. In either
case, care can be taken to make sure that the tag that's caught and the tag
that's thrown are EQ.
There *are* some performance penalties for portability, you know....
Yeah, but Common Lisp tries to give a reasonable amount of flexibility to the
implementor. Given the whole EQ not working on numbers business, I don't think
there's much more cognitive load on the programmer.
It's probably time for people to start realizing that there are real Common
Lisp implementations supporting real users Right Now. Take a look at the
Stability paragraph on page 3.