-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Daniel Kraft wrote: > Hi, > > thanks for your comments; I'm still a bit confused, though :$ > > Marijn Schouten (hkBst) wrote: >>> What's about this: >>> >>> (defun test () a) >>> (let ((a 1)) >>> (print a) ; 1 >>> (print (test)) ; 1 >>> (lexical-set! a 2) >> there is only one variable `a' in my mental model, >> so this changes the value of the only `a' and all >> subsequent expressions accessing `a' are thus affected. >> The same as if you had written `(set! a 2)'. Dynamic >> and lexical only differ in how free variables in >> procedures are bound. >>> (print a) ; 1? >> no, (print a) => 2 >>> (print (test)) ; 1 >> no, there is only one `a' and its value is 2 here >>> (print (lexical a)) ; 2 >>> ) > > Hm... my problem is trying to understand how you want this implemented; > my main point about lexical scoping is that it enables us to use Guile's > built-in lexical mechanisms and we don't have to save the value > explicitly into some fluids. > > But if you require that the second (print (test)) above prints 1 even > though we have done (lexical-set! a) this means that lexical-set! must > update the place somehow where a is accessed dynamically (as is done in > test). And that seems to imply that this lexical-set! updates the > fluids, even though it is meant to perform on a lexically bound variable > a; just in case that "the one" a is at some place referred to dynamically.
In my proposal it is meaningless to say "lexically bound variable", as all variables would in principal be accessible both lexically and dynamically. >>> I don't think it's good to have to "completely seperate" variables a and >>> (lexical a). >> >> I don't understand what you mean. My proposal is to have one kind of >> variable >> and two kinds of access. > > Can you please elaborate on this? If there's only one variable and only > the value 2 after the lexical-set! above (both for (print a) in the > lexical scope and (print (test)) which accesses a dynamically), what > would then be the point of writing 'a' or '(lexical a)' and what would > be the difference between those two? (defvar x 3) (defun dynx () x) (dynx) ; => 3 (defun lexx () (lexical x)) (lexx) ; => 3 (defun incdynx () (setq x (+ x 1))) (defun inclexx () (lexical-setq x (+ (lexical x) 1))) (let ((x 5)) (dynx) ; => 5 (lexx) ; => 3 (lexical-setq x 6) (dynx) ; => 6 (lexx) ; => 3 (setq x 7) (dynx) ; => 7 (lexx) ; => 3 (incdynx) (dynx) ; => 8 (lexx) ; => 3 (inclexx) (dynx) ; => 8 (lexx) ; => 4 ) (dynx) ; => 4 (lexx) ; => 4 (incdynx) (dynx) ; => 5 (lexx) ; => 5 (inclexx) (dynx) ; => 6 (lexx) ; => 6 I hope I haven't made any mistakes there and that it explains what I have in mind. Marijn - -- If you cannot read my mind, then listen to what I say. Marijn Schouten (hkBst), Gentoo Lisp project, Gentoo ML <http://www.gentoo.org/proj/en/lisp/>, #gentoo-{lisp,ml} on FreeNode -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.11 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iEYEARECAAYFAkpplk8ACgkQp/VmCx0OL2wFVACfV36PIQRwjQu3gGOc8Rly6h8Z UKQAnA5yPPMBNJsoRoc70+5znTP10r6G =SL2/ -----END PGP SIGNATURE-----
