On 7/21/19 10:41 PM, Tim Meehan wrote:
When hovering over names in a program that I downloaded to examine, I
noticed a purple question mark that I had not remembered seeing before.
I am used to hovering over a name and seeing where else it is used,
etc., but I don't remember seeing the purple question mark before ...
I searched for DrRacket documentation in the "Racket Documentation" app,
and also at Northwestern
<https://plt.eecs.northwestern.edu/snapshots/current/pdf-doc/drracket.pdf>,
but didn't see anything that described it. I'm going to try and attach a
screenshot - but I am not sure that it will survive the mailing list
process. In case it does not survive, I was looking at Matthias
Felleisen's implementation of the 7GUIs tasks, specifically, task-2.rkt
<https://raw.githubusercontent.com/mfelleisen/7GUI/master/task-2.rkt>. I
was hovering over "render" in line 27. The question mark shows up when
pointing to the usage of "render" on line 25. I suppose that if I had to
guess, it might have something to do with the usage being in a
"define-syntax-rule."
Yes. The purple arrow is drawn to identifiers in syntax constants
(things that eventually wind up in a quote-syntax form). It's different
from a blue arrow because it shows a *potential* reference, but
depending on how the syntax is used it may or may not turn into an
actual reference.
Here's a simple example that shows potential references to `x` (with
purple arrows) that do not become actual references:
#lang racket
(define x 12)
(define-syntax-rule (id)
(lambda (x) x))
Ryan
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