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definition of lexical closure
- To: common-lisp@SU-AI.ARPA
- Subject: definition of lexical closure
- From: PGS%MIT-OZ@MIT-MC.ARPA
- Date: Tue, 29 Jan 1985 10:34:00 -0000
- In-reply-to: Msg of 27 Jan 1985 19:57-EST from PGS
Date: Sunday, 27 January 1985 19:57-EST
To: common-lisp at SU-AI.ARPA
Re: definition of lexical closure
I was talking to someone today about the Common Lisp notion of a closure,
and I noticed that the definition of a lexical closure on page 87 of the
CL manual is sort of vague and unsatisfactory. It says that a lexical
closure is the object returned by FUNCTION, that is, a function which,
when invoked, obeys the rules for lexical scoping.
The problem with this definition is that it makes it difficult to explain
why the thing referred to is called a closure. It's hard to relate the
definition even vaguely to the set-theoretic notion of a closure, because
it doesn't describe a set, so one can't explain the term as coming from
the notion of `closing over' a set of bindings...
Oops, I take it all back. I dug out my copy of Kleene and found that I
really wanted the predicate calculus notion of closure, not the set-theoretic
notion of closure.