The printer tries to produce an expression that you could copy, paste, and
evaluate. Transparent structs aren't quotable but do support
constructor-style printing, so the printer uses constructor-style printing
for values that contain transparent structs. (Apparently you can configure
this in DrRacket to use e.g. quasiquotation if you prefer:
https://docs.racket-lang.org/drracket/output-syntax.html) Since opaque
structs don't support any nice printing behavior by default, the printer
gives up and uses the more concise quoted form with the non-expression
printed form of the opaque value.
The docs for prop:custom-print-quotable and gen:custom-write and the
Reference section on The Printer
<https://docs.racket-lang.org/reference/printing.html> have more technical
On Tue, May 16, 2017 at 9:21 AM, Dan Grossman <d...@cs.washington.edu> wrote:
> Hi all,
> In my course here on campus, I have students use #lang racket and we put
> #:transparent on our struct definitions for easier REPL interactions. A
> student was confused by the different printer-behavior between a and b in
> the attached screenshot, and I can't think of a reason for the different
> behavior for b compared to a and c either. Curious if there /is/ a decent
> reason or if this is just one of those glitches.
> "No big deal" but worth asking...
> [image: Inline image 1]
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