[racket] print/pretty-print weirdness

Greetings again.

I'm still hoping for some help from you friendly bunch of geniuses!

Lest you think that the printing weirdness I described in my previous email is relegated to that world of Racket OOP classes and objects, please look at this example which uses only struct values:

	#lang racket
	
	(struct test-printable []
	  #:property prop:custom-print-quotable 'never
	  #:methods gen:custom-write
	  [(define [write-proc strct port mode]
	     (when {eqv? mode 1}
	       {error "test-printable printed with depth of 1"} )
	     {fprintf port "(test-printable ~v)" {list {test-printable2}}} )])
	
	(struct test-printable2 []
	  #:property prop:custom-print-quotable 'never
	  #:methods gen:custom-write
	  [(define [write-proc strct port mode]
	     (when {eqv? mode 1}
	       {error "test-printable2 printed with depth of 1"} )
	     {display "(test-printable2)" port} )])

Here is an interactions session:

	> {test-printable2} 
	(test-printable2) 

	> {list {test-printable2}} 
	(list (test-printable2)) 

	> {test-printable} ; produces error
	 . . test-printable2 printed with depth of 1


What I want is for the third expression line to print the below:

	(test-printable (list (test-printable2)))

But as you can see, that is not what happens. I don't understand why it does what it's doing. Furthermore, is there a solution can I use to get print to write stuff out without forcing it to be quoted when it isn't supposed to be?

By the way, if I change the above code so that print is explicitly at quote depth of 0, print ignores it and calls the write-proc handler with quote depth of 1 anyway, thus giving the same error:

	(struct test-printable []
	  #:property prop:custom-print-quotable 'never
	  #:methods gen:custom-write
	  [(define [write-proc strct port mode]
	     (when {eqv? mode 1}
	       {error "test-printable printed with depth of 1"} )
	     {display "(test-printable " port}
	     {print {list {test-printable2}} port 0} ; explicitly at quote depth of 0 but is IGNORED!
	     {display ")" port} )])

	> {test-printable} ; still produces error
	 . . test-printable2 printed with depth of 1

I would love you hear back from someone in the know. Many thanks!

--Christopher



On Nov 5, 2013, at 12:09 PM, Christopher <ultimatemacfanatic at gmail.com> wrote:

> I'm experiencing some weirdness with print and pretty-print.
> 
> First of all, can someone please explain why these print the same thing:
> 
> > (print 'hello (current-output-port) 0)
> 'hello
> > (print 'hello (current-output-port) 1)
> 'hello
> 
> But these do not:
> 
> > (pretty-print 'hello (current-output-port) 0)
> 'hello
> > (pretty-print 'hello (current-output-port) 1)
> hello
> 
> (notice the bottom line has no quote in front of the symbol)
> 
> It seems to me that (print 'hello (current-output-port) 1) should not print with a single-quote in front of the symbol, but it does, as you can see above.
> 
> 
> Consider this:
> 
> #lang racket
> 
> (define allow-quoted #t)
> 
> (define printable-unquoted<%>
>   (interface* []
>     [[prop:custom-print-quotable 'never]
>      [prop:custom-write 
>        (lambda (obj port mode)
>          (cond
>            [{eq? mode #t} (send obj custom-write port)]
>            [{eq? mode #f} (send obj custom-display port)]
>            [(or {= mode 0} allow-quoted) (send obj custom-print port)]
>            [{= mode 1} {error {string-append "printable-unquoted<%> object "
>                                       "called with depth of 1" }}]))]]
>      custom-write custom-display custom-print ))
> 
> (define test-printable%
>   (class* object% [printable-unquoted<%>]
>     (super-make-object)
>     
>     (define/public [custom-print port]
>       {display "(make-object test-printable%)" port} )
>     
>     (define/public [custom-write port]
>       {display "|;-)" port} )
>     
>     (define/public [custom-display port]
>       {custom-write port} ))) 
> 
> (struct test-printable []
>   #:property prop:custom-print-quotable 'never
>   #:methods gen:custom-write
>   [(define [write-proc strct port arg]
>      {fprintf port "(test-printable ~v)" {vector (new test-printable%)}} )])
> 
> 
> {print {test-printable}}
> 
> If I run it with (define allow-quoted #t) then the result is:
> 
> (test-printable '#((make-object test-printable%)))
> 
> Notice that the declared unquotable object is printed in the middle of a quoted vector!!
> 
> If I set allow-quoted to #f then we confirm the obvious:
> 
> (test-printable '#(. . printable-unquoted<%> object called with depth of 1
> 
> Can anyone tell me why my prop:custom-print-quotable 'never is not being respected on my class instance?
> 
> Thanks,
> 
> Christopher