#144 symbol-macrolet not always expanded
Some obsure macroexpand or walker problem.
SYMBOL-MACROLET doesn't always expand.
(in-package "FFI")
(setq fx (ffi::lookup-foreign-variable
"ffi_user_pointer" (ffi::parse-c-type '(c-array
character 4))))
;-> #<FOREIGN-VARIABLE "ffi_user_pointer" #x00668C0C>
(defmacro with-foreign-var ((var fvar) &body body)
(let ((fv (gensym (symbol-name var))))
`(LET ((,fv ,fvar))
(SYMBOL-MACROLET ((,var (FOREIGN-VALUE ,fv)))
,@body))))
(with-foreign-var (x fx) (typeof x))
*** - TYPEOF is only allowed after FOREIGN-VALUE:
(TYPEOF X)
(with-foreign-var (x fx) (identity (typeof x)))
;-> (C-ARRAY CHARACTER 4)
(with-foreign-var (x fx) (element x 0))
*** - ELEMENT is only allowed after FOREIGN-VALUE:
(ELEMENT X 0)
(with-foreign-var (x fx) (values (element x 0)))
;-> #\Null
(with-foreign-object (fv '(c-array-max character 4)
"ab")
(with-foreign-var (x fv) (typeof x)))
;-> (C-ARRAY-MAX CHARACTER 4)
; works even without identity!?!
BTW, if somebody wants to suggest a better name?
; WITH-C-VAR is like a composition of
WITH-FOREIGN-OBJECT and WITH-FOREIGN-VAR
Using CLISP-2.28 built with MS-VC6
Regards,
Jörg Höhle.
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typeof signals the above error at macroexpansion time.
typeof must be macroexpanded before x is replaced by its
symbol-macro expansion.
you will need to modify typeof -- and all the others like it...
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I don't understand what you mean.
typeof has been macroexpanding its argument for half a
decade (and looks ok to me):
(defmacro typeof (place &environment env)
(setq place (macroexpand place env))
This doesn't look like a FFI bug to me, but a macrolet or
symbol-macrolet one, or perhaps an interpreter bug.
The error message mentioning place obviously shows that the
above macroexpand didn't find that X was a (symbol-)macro.
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It really looks like a bug in the interpreter to me:
(let () (declare (compile)) (with-foreign-var (x fx) (typeof
x)))
WARNING in function #:COMPILED-FORM-36 :
FX is neither declared nor bound,
it will be treated as if it were declared SPECIAL.
(C-ARRAY CHARACTER 4)
No bogus error, it works in compiled mode.
(locally (declare (compile)) (with-foreign-var (x fx)
(typeof x))) works
(locally (with-foreign-var (x fx) (typeof x))) breaks
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ok, this IS a bug in typeof (foreign1.lisp).
look at
<http://www.lisp.org/HyperSpec/Body/fun_macroexpa_acroexpand-1.html>:
(let ((x (list 1 2 3)))
(symbol-macrolet ((a (first x)))
(macroexpand 'a)))
A, false
i.e., macroexpand DOES NOT pick up the symbol-macrolet
expansions.
macroexpand should be replaced with expand-form (which does).
please try that the report your experience here.
thank you.
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Your counterexample is broken.
There is no way MACROEXPAND can pick up symbol-macrolet or
macrolet expansions without being given a second argument:
the environment.
The TYPEOF etc. macros do obtain and pass &environment.
I'm wondering what expand-form is that you mention. It's not
in CLHS and my clisp 2.28 says
FFI[13]> (apropos "expand-form")
SYSTEM::%EXPAND-FORM function
SYSTEM::MACROEXPAND-FORM function
I have doubts that the perfectly (to me) legal CL code using
symbol-macrolet, macroexpand etc. needs CLISP specific
extensions to work.
Now I remember that one year ago, I hit this same kind of
error when introducing C-VAR-ADDRESS into foreign1.lisp. I
vaguely remember that it seemed to disappear after I got
that macro with the other ones like typeof into the file,
instead of using interactive definitions. Back then, I
apparently did not file a bug report.
BTW, something maybe strange I just noticed: init.lisp
defines %expand-form and dispatches using #+/-COMPILER.
However, in final image generation (using only .fas),
"compiler" is loaded far after that DEFUN place, so it is
the #-compiler section that gets defined. Is this intended?
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can you give me a self-contained test case which does not
reference FFI?
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Here's code which I arbitrarily put into package FFI, but
does not need it.
(in-package "FFI")
(defmacro with-foreign-var ((var fvar) &body body)
(let ((fv (gensym (symbol-name var))))
`(LET ((,fv ,fvar))
(SYMBOL-MACROLET ((,var (FOREIGN-VALUE ,fv)))
,@body))))
;(with-foreign-var (x "fake foreign variable") (ffi:typeof
x)) breaks
(defmacro my-typeof (place &environment env)
(let ((exp-place (macroexpand place env)))
(format t "MY-TYPEOF expansion: ~S~%" exp-place)
(unless (and (consp exp-place)
(eq (car exp-place) 'FOREIGN-VALUE))
(error "MY-TYPEOF not upon a place: ~S" exp-place))
`(format t "Foreign type from ~S~%" ,(second
exp-place))))
;(macroexpand-1 '(my-typeof x)) -> error
;(macroexpand-1 '(my-typeof (foreign-value x)))
;(with-foreign-var (x "fake foreign variable") (my-typeof
x))
; sometimes works non-reproducibly:
1. Break FFI[69]>
MY-TYPEOF expansion: (FOREIGN-VALUE #:X1834)
MY-TYPEOF expansion: (FOREIGN-VALUE #:X1835)
Foreign type from "fake foreign variable"
NIL
; but usually
FFI[72]>
MY-TYPEOF expansion: X
*** - MY-TYPEOF not upon a place: X
While embedding inside progn, identity or even with multiple
forms makes the code work:
;(with-foreign-var (x "fake foreign variable") (identity
(my-typeof x)))
FFI[86]> MY-TYPEOF expansion: (FOREIGN-VALUE #:X1843)
Foreign type from "fake foreign variable"
NIL
;(with-foreign-var (x "fake foreign variable") 1 (my-typeof
x)) works
;(with-foreign-var (x "fake foreign variable") "ab"
(my-typeof x)) breaks
;(with-foreign-var (x "fake foreign variable") (progn
(my-typeof x))) works
Exactly as with typeof in the original bug report.
I find the "ab" (my-typeof x) case revealing: obviously "ab"
is
ignored, but it doesn't seem to be treated as a
documentation string
either, since adding one of the above progn, identity or
list wrappers
leads to:
;(with-foreign-var (x "fake foreign variable") "ab" (progn
(my-typeof x)))
*** - SYMBOL-MACROLET: doc-strings are not allowed here:
("ab" (PROGN (MY-TYPEOF X)))
Maybe that's a hint, may be a red herring.
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thank you for your bug report.
the bug has been fixed in the CVS tree.
you can either wait for the next release (recommended)
or check out the current CVS tree (see http://clisp.cons.org\)
and build CLISP from the sources (be advised that between
releases the CVS tree is very unstable and may not even build
on your platform).