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Another question about lexical closures

    Date: 15 May 1985 0213-PDT
    From: Rem@IMSSS

    There's a little ambiguity about when two bindings are "the same" and when
    they are "different" bindings. If you bind exactly the same lexical variable
    (in the same function or other executable form) to exactly the same value
    (the values are EQ), at two different times, are the two bindings you get
    considered to be the same or different? 
The way I think of this is "Two calls to LET produce two different
bindings".  So if I read your question right, the answer is "different".

					    I.e. if you make a lexical closure
    in function FOO with X bound to NIL and then make another lexical closure
    in function FOO with X bound to NIL, will the X-variables in those two
    closures be the same variable (sharing side-effects) or not? 

I assume here you mean two calls to FOO, not something like

(LET ((X 5))
  (VALUES #'(LAMBDA () X) #'(LAMBDA (Y) (SETQ X Y))))

where the answer is "save variable (sharing side effects)"

								 My guess
    is they will be different, that is each time you go into a lambda-binding
    you get a "different" binding even if the lexical variable and its value
    are the same both times. Am I correct? 

					   (Note the example at the bottom of
    page 87 doesn't answer this question since TWO-FUNS is called only once.

Indeed, I think this section could use a bit more exposition and further
examples.  I think the manual can't help being a bit of a language
tutorial here, and should abandon the tersness of a reference manual,
even if it ends up repeating the same concept in different ways.

    If it got called a second time, with exactly the same args, and the result
    SETQ'd to global FUNS2, would (CAR FUNS) and (CAR FUNS2) share their
    lexical-closure-variable, i.e. "the binding of the variable X created
    on entry to the function TWO-FUNS when it was called with argument 6"
    as described at the bottom of the page? That phrasing indicates there
    WOULD be sharing, but due to what it says on page 37 top "it depends
    on the invocaton during which the reference is made" I think it WOULD NOT
    be sharing, i.e. wording on page 87 should really say "... on that particular
    entry to the function TWO-FUNS ..." even though in that example it is moot
    since TWO-FUNS was called only once in the example.)
That's right.  There would be sharing between (CAR FUNS) and (CADR FUNS), and
between (CAR FUNS2) and (CADR FUNS2), but not between the elements of FUNS
and FUNS2.