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 12 hours ago
Drew
48.6k463107
asked 17 hours ago
phsphs
522212
add a 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 12 hours ago
Drew
48.6k463107
asked 17 hours ago
phsphs
522212
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
16 hours ago
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
16 hours ago
1
You might like to play withprint-gensymto better see what's going on.
– Stefan
13 hours ago
@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
12 hours ago
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
7 hours ago
add a 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 12 hours ago
Drew
48.6k463107
asked 17 hours ago
phsphs
522212
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 12 hours ago
Drew
48.6k463107
asked 17 hours ago
phsphs
522212
edited 12 hours ago
Drew
48.6k463107
asked 17 hours ago
phsphs
522212
edited 12 hours ago
Drew
48.6k463107
edited 12 hours ago
Drew
48.6k463107
edited 12 hours ago
Drew
48.6k463107
48.6k463107
asked 17 hours ago
phsphs
522212
asked 17 hours ago
phsphs
522212
asked 17 hours ago
phsphs
522212
522212
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
16 hours ago
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
16 hours ago
1
You might like to play withprint-gensymto better see what's going on.
– Stefan
13 hours ago
@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
12 hours ago
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
7 hours ago
add a 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
16 hours ago
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
16 hours ago
1
You might like to play withprint-gensymto better see what's going on.
– Stefan
13 hours ago
@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
12 hours ago
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
7 hours ago
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
16 hours ago
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
16 hours ago
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
16 hours ago
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
16 hours ago
1
1
You might like to play with
print-gensym to better see what's going on.– Stefan
13 hours ago
You might like to play with
print-gensym to better see what's going on.– Stefan
13 hours ago
@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
12 hours ago
@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
12 hours ago
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
7 hours ago
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
7 hours ago
add a comment |
1 Answer
1
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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 16 hours ago
philsphils
27.6k23769
1
Worth noting that settingprint-gensymandprint-circletotproduces a printed representation which can read back to something equivalent.
– npostavs
3 hours ago
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 16 hours ago
philsphils
27.6k23769
1
Worth noting that settingprint-gensymandprint-circletotproduces a printed representation which can read back to something equivalent.
– npostavs
3 hours ago
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 16 hours ago
philsphils
27.6k23769
1
Worth noting that settingprint-gensymandprint-circletotproduces a printed representation which can read back to something equivalent.
– npostavs
3 hours ago
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 16 hours ago
philsphils
27.6k23769
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 16 hours ago
philsphils
27.6k23769
answered 16 hours ago
philsphils
27.6k23769
answered 16 hours ago
philsphils
27.6k23769
answered 16 hours ago
philsphils
27.6k23769
27.6k23769
1
Worth noting that settingprint-gensymandprint-circletotproduces a printed representation which can read back to something equivalent.
– npostavs
3 hours ago
add a comment |
1
Worth noting that settingprint-gensymandprint-circletotproduces a printed representation which can read back to something equivalent.
– npostavs
3 hours ago
1
1
Worth noting that setting
print-gensym and print-circle to t produces a printed representation which can read back to something equivalent.– npostavs
3 hours ago
Worth noting that setting
print-gensym and print-circle to t produces a printed representation which can read back to something equivalent.– npostavs
3 hours ago
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
16 hours ago
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
16 hours ago
1
You might like to play with
print-gensymto better see what's going on.– Stefan
13 hours ago
@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
12 hours ago
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
7 hours ago