How do I associate mangled identifiers with the original syntax?

Questions & Answers
1

Hi, Racket Discourse.

I am busy working on a macro that, among other things, expands into a struct with certain fields being made up of concatenations via . of the original syntax.

As an example, we have this little definition below, and some of the field accessors generated by the resulting struct.

image
image639×366 25.5 KB

Note how the original syntax is associated with the resulting field accessor.

Now, because the path parameter ip.geo is a compound, it is not the original syntax so is not associated in the same manner to the original geo.

I have taken a shallow look at define-struct.rkt but it is a hefty one. What in particular am I supposed to be looking at, to achieve this? Rename-transformers, maybe syntax source location data, are the vague directions I think I am headed to?

It's not super critical, I am just curious how that would be accomplished.

3 Likes
2

(From memory) you might be looking for something called sub-range-binders? I think format-id has some support for that.

3 Likes
3

That's really cool, thank you, @benknoble :grin:

I will have to mess around a bit to see what's what, but now I can look for examples of what others have done!

Edit: dit werk!

image
image802×536 36.9 KB

All that was needed (in this case), as @benknoble mentioned, was this:

(format-id stx "~a:~a" api-id name #:subs? #true)
2 Likes
4

As I've just reminded myself, sometimes what you want is actually to use #:source and the 'original-for-check-syntax property. Example:

#lang racket

(require syntax/parse/define
         (for-syntax racket/syntax))

(define-syntax-parser define-f*
  [(_ f:id)
   #:with f* (format-id #'f "~a*" #'f)
   #'(define f* 1)])

(define-f* g)
g*

DrRacket doesn't draw any arrows here. With #:subs? #t, we get an arrow from g in g* to the input g to the macro.

But what if we want an arrow from g* (the entire identifier) to the g in the macro? For that, we should use #:source #'f and the syntax property I mentioned (which is one of 2 ways DrRacket draws arrows; the other is for syntax-original? syntax), and we should omit #:subs? (or things get confused):

#lang racket

(require syntax/parse/define
         (for-syntax racket/syntax))

(define-syntax-parser define-f*
  [(_ f:id)
   #:with f* (syntax-property (format-id #'f #:source #'f "~a*" #'f)
                              'original-for-check-syntax #t)
   #'(define f* 1)])

(define-f* g)
g*

Now we have an arrow from g* to g, rather than just g to g.

This matters a bit more when building prefixed IDs, I think:

  • If a-b-c is derived from b with #:subs? arrows, then the only place my editor can jump-to-definition is when on b in a-b-c.
  • However, if a-b-c is derived from b with #:source + 'original-for-check-syntax arrows, then my editor can jump-to-definition from anywhere in a-b-c because the whole identifier gets the arrow.
2 Likes