Setf weird expansion
Trying to understand what setf can do, I called
(macroexpand '(setf (aref vec i) val))
⇒ (let* ((v vec) (v i)) (aset v v val))
This seems obviously wrong.
However I couldn't create an actual instance where (setf (aref .. fails. E.g.
(setq vec (make-vector 10 nil) i 3 val 'foo)
⇒ foo
(setf (aref vec i) val)
⇒ foo
vec
⇒ [nil nil nil foo nil nil nil nil nil nil]
Can someone explain what is going on here?
elisp-macros setf
edited Mar 11 at 13:40
Drew
48.8k463107
asked Mar 11 at 8:40
phsphs
534212
|
show 1 more comment
Trying to understand what setf can do, I called
(macroexpand '(setf (aref vec i) val))
⇒ (let* ((v vec) (v i)) (aset v v val))
This seems obviously wrong.
However I couldn't create an actual instance where (setf (aref .. fails. E.g.
(setq vec (make-vector 10 nil) i 3 val 'foo)
⇒ foo
(setf (aref vec i) val)
⇒ foo
vec
⇒ [nil nil nil foo nil nil nil nil nil nil]
Can someone explain what is going on here?
elisp-macros setf
edited Mar 11 at 13:40
Drew
48.8k463107
asked Mar 11 at 8:40
phsphs
534212
2
OK. I understand now. The twovsymbols are not the same and(let* ((form (macroexpand '(setf (aref vec i) val))) (symb1 (caar (cadr form))) (symb2 (caar (cdadr form)))) (equal symb1 symb2))returnsnil.
– phs
Mar 11 at 9:58
1
Strangely, the code forsetfin source filegv.elseems to create thevsymbols with a vanilla use of(gensym "v")and this should append a counter value after the "v" prefix, creating uninterned symbolsv0,v1,v2, etc.
– phs
Mar 11 at 10:05
2
You might like to play withprint-gensymto better see what's going on.
– Stefan
Mar 11 at 12:35
@stefan: I have emacs-26.1 and it has noprint-gensymAFAICT :-( Does anyone have an explanation why the(gensym "v")in source filegv.eldoes not appendgensym-counter?!
– phs
Mar 11 at 13:59
1
I'm pretty sure you do haveprint-gensym, you likely just looked at the wrong place (tryC-h oinstead ofC-h f). Thelet*in your expanded code is likely generated bymacroexp-let2which usesmake-symbolrather thangensym.
– Stefan
Mar 11 at 19:01
|
show 1 more comment
Trying to understand what setf can do, I called
(macroexpand '(setf (aref vec i) val))
⇒ (let* ((v vec) (v i)) (aset v v val))
This seems obviously wrong.
However I couldn't create an actual instance where (setf (aref .. fails. E.g.
(setq vec (make-vector 10 nil) i 3 val 'foo)
⇒ foo
(setf (aref vec i) val)
⇒ foo
vec
⇒ [nil nil nil foo nil nil nil nil nil nil]
Can someone explain what is going on here?
elisp-macros setf
edited Mar 11 at 13:40
Drew
48.8k463107
asked Mar 11 at 8:40
phsphs
534212
Trying to understand what setf can do, I called
(macroexpand '(setf (aref vec i) val))
⇒ (let* ((v vec) (v i)) (aset v v val))
This seems obviously wrong.
However I couldn't create an actual instance where (setf (aref .. fails. E.g.
(setq vec (make-vector 10 nil) i 3 val 'foo)
⇒ foo
(setf (aref vec i) val)
⇒ foo
vec
⇒ [nil nil nil foo nil nil nil nil nil nil]
Can someone explain what is going on here?
elisp-macros setf
elisp-macros setf
edited Mar 11 at 13:40
Drew
48.8k463107
asked Mar 11 at 8:40
phsphs
534212
edited Mar 11 at 13:40
Drew
48.8k463107
asked Mar 11 at 8:40
phsphs
534212
edited Mar 11 at 13:40
Drew
48.8k463107
edited Mar 11 at 13:40
Drew
48.8k463107
edited Mar 11 at 13:40
Drew
48.8k463107
48.8k463107
asked Mar 11 at 8:40
phsphs
534212
asked Mar 11 at 8:40
phsphs
534212
asked Mar 11 at 8:40
phsphs
534212
534212
2
OK. I understand now. The twovsymbols are not the same and(let* ((form (macroexpand '(setf (aref vec i) val))) (symb1 (caar (cadr form))) (symb2 (caar (cdadr form)))) (equal symb1 symb2))returnsnil.
– phs
Mar 11 at 9:58
1
Strangely, the code forsetfin source filegv.elseems to create thevsymbols with a vanilla use of(gensym "v")and this should append a counter value after the "v" prefix, creating uninterned symbolsv0,v1,v2, etc.
– phs
Mar 11 at 10:05
2
You might like to play withprint-gensymto better see what's going on.
– Stefan
Mar 11 at 12:35
@stefan: I have emacs-26.1 and it has noprint-gensymAFAICT :-( Does anyone have an explanation why the(gensym "v")in source filegv.eldoes not appendgensym-counter?!
– phs
Mar 11 at 13:59
1
I'm pretty sure you do haveprint-gensym, you likely just looked at the wrong place (tryC-h oinstead ofC-h f). Thelet*in your expanded code is likely generated bymacroexp-let2which usesmake-symbolrather thangensym.
– Stefan
Mar 11 at 19:01
|
show 1 more comment
2
OK. I understand now. The twovsymbols are not the same and(let* ((form (macroexpand '(setf (aref vec i) val))) (symb1 (caar (cadr form))) (symb2 (caar (cdadr form)))) (equal symb1 symb2))returnsnil.
– phs
Mar 11 at 9:58
1
Strangely, the code forsetfin source filegv.elseems to create thevsymbols with a vanilla use of(gensym "v")and this should append a counter value after the "v" prefix, creating uninterned symbolsv0,v1,v2, etc.
– phs
Mar 11 at 10:05
2
You might like to play withprint-gensymto better see what's going on.
– Stefan
Mar 11 at 12:35
@stefan: I have emacs-26.1 and it has noprint-gensymAFAICT :-( Does anyone have an explanation why the(gensym "v")in source filegv.eldoes not appendgensym-counter?!
– phs
Mar 11 at 13:59
1
I'm pretty sure you do haveprint-gensym, you likely just looked at the wrong place (tryC-h oinstead ofC-h f). Thelet*in your expanded code is likely generated bymacroexp-let2which usesmake-symbolrather thangensym.
– Stefan
Mar 11 at 19:01
2
2
OK. I understand now. The two
v symbols are not the same and (let* ((form (macroexpand '(setf (aref vec i) val))) (symb1 (caar (cadr form))) (symb2 (caar (cdadr form)))) (equal symb1 symb2)) returns nil.– phs
Mar 11 at 9:58
OK. I understand now. The two
v symbols are not the same and (let* ((form (macroexpand '(setf (aref vec i) val))) (symb1 (caar (cadr form))) (symb2 (caar (cdadr form)))) (equal symb1 symb2)) returns nil.– phs
Mar 11 at 9:58
1
1
Strangely, the code for
setf in source file gv.el seems to create the v symbols with a vanilla use of (gensym "v") and this should append a counter value after the "v" prefix, creating uninterned symbols v0, v1, v2, etc.– phs
Mar 11 at 10:05
Strangely, the code for
setf in source file gv.el seems to create the v symbols with a vanilla use of (gensym "v") and this should append a counter value after the "v" prefix, creating uninterned symbols v0, v1, v2, etc.– phs
Mar 11 at 10:05
2
2
You might like to play with
print-gensym to better see what's going on.– Stefan
Mar 11 at 12:35
You might like to play with
print-gensym to better see what's going on.– Stefan
Mar 11 at 12:35
@stefan: I have emacs-26.1 and it has no
print-gensym AFAICT :-( Does anyone have an explanation why the (gensym "v") in source file gv.el does not append gensym-counter ?!– phs
Mar 11 at 13:59
@stefan: I have emacs-26.1 and it has no
print-gensym AFAICT :-( Does anyone have an explanation why the (gensym "v") in source file gv.el does not append gensym-counter ?!– phs
Mar 11 at 13:59
1
1
I'm pretty sure you do have
print-gensym, you likely just looked at the wrong place (try C-h o instead of C-h f). The let* in your expanded code is likely generated by macroexp-let2 which uses make-symbol rather than gensym.– Stefan
Mar 11 at 19:01
I'm pretty sure you do have
print-gensym, you likely just looked at the wrong place (try C-h o instead of C-h f). The let* in your expanded code is likely generated by macroexp-let2 which uses make-symbol rather than gensym.– Stefan
Mar 11 at 19:01
|
show 1 more comment
1 Answer
1
active
oldest
votes
From your comment you've figured this out for yourself, but...
In the macro expansion you're seeing the printed representation of two independent symbols with the same name. Most likely both of those symbols are uninterned.
A printed representation like this, if passed back to the lisp reader, would not be equivalent to the original, as the lisp reader would intern the symbols.
This is similar to:
(list (make-symbol "v") (make-symbol "v"))
(v v)
answered Mar 11 at 10:16
philsphils
27.8k23769
3
Worth noting that settingprint-gensymandprint-circletotproduces a printed representation which can read back to something equivalent.
– npostavs
Mar 11 at 22:31
add a comment |
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From your comment you've figured this out for yourself, but...
In the macro expansion you're seeing the printed representation of two independent symbols with the same name. Most likely both of those symbols are uninterned.
A printed representation like this, if passed back to the lisp reader, would not be equivalent to the original, as the lisp reader would intern the symbols.
This is similar to:
(list (make-symbol "v") (make-symbol "v"))
(v v)
answered Mar 11 at 10:16
philsphils
27.8k23769
3
Worth noting that settingprint-gensymandprint-circletotproduces a printed representation which can read back to something equivalent.
– npostavs
Mar 11 at 22:31
add a comment |
From your comment you've figured this out for yourself, but...
In the macro expansion you're seeing the printed representation of two independent symbols with the same name. Most likely both of those symbols are uninterned.
A printed representation like this, if passed back to the lisp reader, would not be equivalent to the original, as the lisp reader would intern the symbols.
This is similar to:
(list (make-symbol "v") (make-symbol "v"))
(v v)
answered Mar 11 at 10:16
philsphils
27.8k23769
3
Worth noting that settingprint-gensymandprint-circletotproduces a printed representation which can read back to something equivalent.
– npostavs
Mar 11 at 22:31
add a comment |
From your comment you've figured this out for yourself, but...
In the macro expansion you're seeing the printed representation of two independent symbols with the same name. Most likely both of those symbols are uninterned.
A printed representation like this, if passed back to the lisp reader, would not be equivalent to the original, as the lisp reader would intern the symbols.
This is similar to:
(list (make-symbol "v") (make-symbol "v"))
(v v)
answered Mar 11 at 10:16
philsphils
27.8k23769
From your comment you've figured this out for yourself, but...
In the macro expansion you're seeing the printed representation of two independent symbols with the same name. Most likely both of those symbols are uninterned.
A printed representation like this, if passed back to the lisp reader, would not be equivalent to the original, as the lisp reader would intern the symbols.
This is similar to:
(list (make-symbol "v") (make-symbol "v"))
(v v)
answered Mar 11 at 10:16
philsphils
27.8k23769
answered Mar 11 at 10:16
philsphils
27.8k23769
answered Mar 11 at 10:16
philsphils
27.8k23769
answered Mar 11 at 10:16
philsphils
27.8k23769
27.8k23769
3
Worth noting that settingprint-gensymandprint-circletotproduces a printed representation which can read back to something equivalent.
– npostavs
Mar 11 at 22:31
add a comment |
3
Worth noting that settingprint-gensymandprint-circletotproduces a printed representation which can read back to something equivalent.
– npostavs
Mar 11 at 22:31
3
3
Worth noting that setting
print-gensym and print-circle to t produces a printed representation which can read back to something equivalent.– npostavs
Mar 11 at 22:31
Worth noting that setting
print-gensym and print-circle to t produces a printed representation which can read back to something equivalent.– npostavs
Mar 11 at 22:31
add a comment |
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2
OK. I understand now. The two
vsymbols are not the same and(let* ((form (macroexpand '(setf (aref vec i) val))) (symb1 (caar (cadr form))) (symb2 (caar (cdadr form)))) (equal symb1 symb2))returnsnil.– phs
Mar 11 at 9:58
1
Strangely, the code for
setfin source filegv.elseems to create thevsymbols with a vanilla use of(gensym "v")and this should append a counter value after the "v" prefix, creating uninterned symbolsv0,v1,v2, etc.– phs
Mar 11 at 10:05
2
You might like to play with
print-gensymto better see what's going on.– Stefan
Mar 11 at 12:35
@stefan: I have emacs-26.1 and it has no
print-gensymAFAICT :-( Does anyone have an explanation why the(gensym "v")in source filegv.eldoes not appendgensym-counter?!– phs
Mar 11 at 13:59
1
I'm pretty sure you do have
print-gensym, you likely just looked at the wrong place (tryC-h oinstead ofC-h f). Thelet*in your expanded code is likely generated bymacroexp-let2which usesmake-symbolrather thangensym.– Stefan
Mar 11 at 19:01