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Re: Opaque syntax objects



On Sun, 14 Aug 2005, [ISO-8859-1] Jens Axel Søgaard wrote:

What should I do if I want to give a piece of (expanded) syntax the
same source information as, say, the macro call?

There can be a primitive for that.  E.g.,
  annotate : (syntax-object, syntax-object) -> syntax-object
In the hash-table, this would insert a new entry for the pair representing the second syntax object, copying the annotation of the first.

Of course. Syntax objects are still ordinary pairs. No change to car/cdr is required. The hash table with source information is kept separately.

Hmm. How do you represent identifiers?

The same way, once you give them a wrap to give them separate identities.

I believe with-syntax behaves that way in order to be (more) compatible
with the psyntax-implementation. Note that the source location
information for stx-expr in

 (with-syntax ((pattern stx-expr) ...) expr)

is taken from stx-expr, when stx-expr is not returning a list. That
is the source location is still tracked.


Do you know what location is assigned when stx-expr is a list?

As an aside, it is sometimes easy to throw away too much information when using the destructuring idiom. For example, in

  (define-syntax let1
    (lambda (form)
      (syntax-case form ()
        ((_ ((i e) ...) e1 e2 ...)
         (syntax (let ((i e) ...) e1 e2 ...))))))

it is unlikely that most implementations would keep the location of the input subnode ((i e) ...) in the result.

Cheers
Andre