On Sat, Jan 7, 2012 at 1:05 AM, Andy Wingo <wingo@pobox.com> wrote:

> On Mon 05 Dec 2011 19:12, Stefan Israelsson Tampe <stefan.itampe@gmail.com>
> writes:
>
> > (define-syntax info
> >   (lambda (x)
> >     (syntax-case x ()
> >       ((_ x)
> >         (pk (syntax-binding-info (syntax->datum #'x)))
> >         #'#f))))
>
> I agree with Ian that we should be operating on syntax objects here, not
> on datums.  Also, what should the type of the return value be?  Racket
> implies that it should be a procedure, no?
>

syntax-binding-info just returns the binding information used at a lookup
in psyntax for an identifier
but it would be better if it returns a lookup procedure that applied to a
syntax object gives the lookuped
information assuming that psyntax is not mutating. using this primitive we
can design a syntax-local-value
according to racket

e.g.
(syntax-local-value id-stx [failure-thunk intdef-ctx]) -> any
  id-stx        : syntax?
  failure-thunk : (or/c (-> any) #f)                          = #f
  intdef-ctx    : (or/c internal-definition-context? #f) = #f

This should return the value of the macro binding that can be anything and
if it's not a macro
eval failure thunk or return #f if not supplied. Also intef-ctx could in
our case be then lookup-function
returned by a call to syntax-binding-info in order to mimic the racket
logic. To note is that in syntax-parse
syntax classes are defined as a macro with a struct value instead of a
transformer. Also to not is that in racket they have special renamer macros
that interacts with this function in such a way that the syntax-local-value
of a renamer macro is following the renamer and calls this function again
on the renamer value
automagically. It should be noted that renamer macros is needed to make
syntax-parse clean in that you long descriptive names for the syntax
classes and it is assumed that you rename them when using the actual syntax
parse.



> > and calling this in an example lead to
> > (let-syntax ((a (lambda (x) #'#f)))
> >       (info a))
>
> Does it work on toplevel macros as well?
>
>
Yes!

/Stefan