I think my confusion stems from the fact that the inner syntax-parse rebinds 'name' but the original source location is preserved so when I print out #'name in the 'make-transformer' macro I see that it still points at the original 'x'. When I print 'new-name' instead I see it has a source location from the inner syntax-parse expression. I was trying to correlate the source location with the lexical context but that doesn't work. Maybe its a bad idea to use the source location to try to infer lexical properties but source location is the only thing printed with printf -- this is why I don't think printf is a good tool to debug macros.
On 05/21/2012 08:04 PM, Matthew Flatt wrote: > I don't understand your objections to the `printf' results, but I think > I can now better explain your original problem. > > When the template has > > (syntax-parse stx > [(_ new-name) > (with-syntax ([output (make-transformer name pattern template)]) > #'(define-syntax new-name output))]) > > then the expansion of > > (define-new-syntax x ... ...) > > has > > (syntax-parse stx > [(_ new-name) > (with-syntax ([output (make-transformer x pattern template)]) > #'(define-syntax new-name output))]) > > There's an `x' as the fist sub-form to `make-transformer', as intended. > > > When the `new-name's are changed to `name' so that the template has > > (syntax-parse stx > [(_ name) > (with-syntax ([output (make-transformer name pattern template)]) > #'(define-syntax name output))]) > > then the expansion of > > (define-new-syntax x ... ...) > > has > > (syntax-parse stx > [(_ x) > (with-syntax ([output (make-transformer x pattern template)]) > #'(define-syntax x output))]) > > Again, `x' appears in as the first sub-form of `make-transformer' --- > but this `x' is bound as a pattern variable by the enclosing > `syntax-parse', which makes it a different `x' than the one when > `new-name' is used in the initial template. > > At Mon, 21 May 2012 11:10:59 -0600, Jon Rafkind wrote: >> On 05/21/2012 10:06 AM, Jon Rafkind wrote: >>> On 05/21/2012 06:02 AM, Matthew Flatt wrote: >>>> At Sun, 20 May 2012 22:42:30 -0600, Jon Rafkind wrote: >>>>> The issue is why do I have to use a name other than 'name' for the >>>>> pattern variable on the line where it says 'HERE'. If I use the >>>>> 'name' pattern variable then the syntax-parse form generated by >>>>> 'make-transformer' will use the wrong lexical context for the literal >>>>> set. I don't see how the lexical context of the outer 'name' differs >>>>> from the inner 'new-name', other than the 'new-name' has an extra >>>>> mark on it. >>>> When you use `name' instead of `new-name', then `name' gets replaced by >>>> `x' from the use of `define-new-syntax', and `x' (unlike `name') has a >>>> different lexical context than `new-name'. >>>> >>> I thought that too but while debugging it didn't seem to be the case. If I >>> put a >> printf in the 'make-transformer' macro to "see" what name is being passed in >> then >> using 'name' or 'new-name' as the pattern variable results in the same thing >> being >> printed. >>> (begin-for-syntax >>> (define-syntax (make-transformer stx) >>> (syntax-parse stx >>> [(_ name pattern template) >>> (printf "Name is ~a\n" #'name) >>> #'#'(lambda (stx) >>> (syntax-parse stx >>> #:literal-sets ([literals #:at name]) >>> [pattern template]))]))) >>> >>> >>> Then calling 'make-transformer' 3 different ways: >>> >>> (lambda (stx) >>> (syntax-parse stx >>> [(_ new-name) >>> (with-syntax ([output (make-transformer name pattern template)]) >>> #'(define-syntax new-name output))] >>> >>> "Name is #<syntax:x.rkt:56:19 x>", where line 56 is the use-site of >> 'define-new-syntax' >>> (lambda (stx) >>> (syntax-parse stx >>> [(_ name) >>> (with-syntax ([output (make-transformer name pattern template)]) >>> #'(define-syntax name output))] >>> "Name is #<syntax:x.rkt:56:19 x>" >> >> I guess this case doesn't print #<syntax:x.rkt:39 x> because the 'name' at >> the >> use-site of 'make-transformer' is not bound by the pattern variable 'name'. >> If that >> is the case then it seems this case should be identical to the 1st case >> where it >> uses a different pattern variable, 'new-name'. >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
