Arrows and syntax parameters

Folks,

I have a simple anaphoric macro, `awhen`, defined as:

-----------------------------------------------------------------------
#lang racket
(require racket/stxparam)

(define-syntax-parameter it
  (λ (stx) (raise-syntax-error #f "use of “it” outside anaphor" stx)))

(define-syntax (awhen stx)
  (syntax-case stx ()
    [(_awhen test body0 body ...)
     #'(let ((t test))
         (syntax-parameterize ([it (syntax-id-rules () [_ t])])
           (when t body0 body ...)))]))

(awhen 32
       (displayln it) ;; [W]
       (awhen 42
              (displayln it))) ;; [X]
-----------------------------------------------------------------------

When I hover over `awhen` in DrRacket, an arrow comes from that
(define-syntax (awhen ...) ...) line, and ends at the instance of
`awhen` I’m over-hovering. The other `awhen` glows green.

When I hover over `it` [W] in DrRacket, an arrow comes from that
(define-syntax-parameter it ...) line, and ends at the instance of `it`
I’m bothering. The other `it` glows green.

I want to tweak the arrows so that when I hover over the first `it` at
[W] I get an arrow pointing wither from 32 (the test) or its `awhen`.

And vice-versa when I hover over an `awhen`.

So I try:
-----------------------------------------------------------------------
(define-syntax (a2when stx)
  (syntax-case stx ()
    [(_a2when test body0 body ...)
     (syntax-property
      #'(let ((t test))
          (syntax-parameterize ([it (syntax-id-rules () [_ t])])
            (when t body0 body ...)))
      'sub-range-binders
      (list
       (vector
        ;; 2 is the length of the identifier "it", 6 of "a2when"
        (syntax-local-introduce #'it) 0 2 0.5 0.5
        (syntax-local-introduce #'_a2when) 0 6 0.5 0.5)))]))

(a2when 32 ;; [P]
        (displayln it) ;; [Y]
        (a2when 42 ;; [Q]
                (displayln it))) ;; [Z]
-----------------------------------------------------------------------

Which has done wonders for my arrows in the past!
But... hovering over either `awhen2` makes all the `awhen2` glow; and
sends arrows out to both `it`, as well as the `it` at [W] and [X]
(I’ve concatenated both code snippets in my source).

I hover over `it` at [Y], and I get all my `it` glowing (and I mean
ALL of them); and arrows into the `it` from the syntax parameter and
BOTH `awhen2`.


Is it possible to get DrRacket to put arrows between [P]->[Y] and
[Q]->[Z] ?


Thanks,

Tim

-- 
Tim Brown CEng MBCS <[email protected]>
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