It's not changing it, I'm just trying to figure out the implementation and understand what I'm seeing. For example, given this:
(struct posn (x y)) (define-syntax (test stx) (syntax-case stx () [(_ x) (printf "val is: ~s" (syntax-local-value #'posn)) #''done])) > posn #<procedure:posn> > (test x) #<procedure:self-ctor-checked-struct-info> I'm surprised that the values are different. Is posn actually always a self-ctor-checked-struct-info object, but it's prop:procedure is defined to allow for being used in an expression in the first case? On Sun, Jan 19, 2014 at 8:40 PM, Carl Eastlund <carl.eastl...@gmail.com>wrote: > If syntax-local-value is returning something other than the value you put > in, that's a bug. It shouldn't be wrapping it or changing it in any way. > Do you have a program where you bind something via define-syntax that > satisfies struct-info?, and get something out via syntax-local-value that > doesn't? > > Carl Eastlund > > On Sun, Jan 19, 2014 at 11:27 PM, Scott Klarenbach <sc...@pointyhat.ca>wrote: > >> But I don't see how the same binding can be a transformer and also return >> something else (like a list, or a checked-struct-info-thing) via >> syntax-local-value. >> >> If I bind my-fn as a transformer, then any other macros that use it with >> syntax-local-value will receive the transformer procedure back, not any >> special meta data. And if I bind it as meta data directly, ie >> (define-syntax my-fn 'something) then it works with syntax-local-value but >> any attempts to use it as a transformer result in illegal syntax. >> >> Even if I create a transformer that returns a struct which implements >> both prop:procedure and prop:struct-info, using that binding with >> syntax-local-value will return the transformer procedure itself, rather >> than the final struct. >> >> >> >> On Sun, Jan 19, 2014 at 8:04 PM, Carl Eastlund >> <carl.eastl...@gmail.com>wrote: >> >>> Yes, I believe that the name of a structure defined by "struct" is bound >>> at syntax-time to a value that implements both prop:procedure, so that it >>> can expand to a use of the constructor when used in an expression, and >>> prop:struct-info so that it can be use to look up static information when >>> passed to relevant macros. >>> >>> Carl Eastlund >>> >>> >>> On Sun, Jan 19, 2014 at 11:00 PM, Scott Klarenbach >>> <sc...@pointyhat.ca>wrote: >>> >>>> How is it that the definition of (struct my-name (x y)) can bind >>>> *my-name* both as a #<procedure:my-name> at runtime and a >>>> transformer-binding *my-name* that at compile time (via >>>> syntax-local-value) produces #<procedure:self-ctor-checked-struct-info>.? >>>> >>>> Or, put another way, how can I define a transformer *my-fn* that >>>> produces syntax, but that also exposes hidden meta-data under the same >>>> binding to other macros that might wish to know about the binding at >>>> compile time? >>>> >>>> I'm specifically wondering how the overloading works. Is it some >>>> clever use of prop:procedure? >>>> >>>> Thanks. >>>> >>>> -- >>>> Talk to you soon, >>>> >>>> Scott Klarenbach >>>> >>>> PointyHat Software Corp. >>>> www.pointyhat.ca >>>> p 604-568-4280 >>>> e sc...@pointyhat.ca >>>> 200-1575 W. Georgia >>>> Vancouver, BC V6G2V3 >>>> >>>> _______________________________________ >>>> To iterate is human; to recur, divine >>>> >>>> ____________________ >>>> Racket Users list: >>>> http://lists.racket-lang.org/users >>>> >>>> >>> >> >> >> -- >> Talk to you soon, >> >> Scott Klarenbach >> >> PointyHat Software Corp. >> www.pointyhat.ca >> p 604-568-4280 >> e sc...@pointyhat.ca >> 200-1575 W. Georgia >> Vancouver, BC V6G2V3 >> >> _______________________________________ >> To iterate is human; to recur, divine >> > > -- Talk to you soon, Scott Klarenbach PointyHat Software Corp. www.pointyhat.ca p 604-568-4280 e sc...@pointyhat.ca 200-1575 W. Georgia Vancouver, BC V6G2V3 _______________________________________ To iterate is human; to recur, divine
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