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 <ultimatemacfana...@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
____________________
Racket Users list:
http://lists.racket-lang.org/users
