Re: [racket-users] Output Port Shenanigans

[Ryan Culpepper]

On 03/14/2018 06:16 PM, Lehi Toskin wrote:


On Wednesday, March 14, 2018 at 10:10:20 AM UTC-7, Matthew Butterick wrote:


probably it requires a combination of peek + read, or copying the
port.


That may be true, but I've been messing around getting *anything* to 
print from inside that function. I'm beginning to think it's never 
actually being run, which leads me to believe this may be a bug.


According to the docs, special-filter is only applied to values written 
using `write-special`. So it is never run on ordinary text.


`write-special` is part of the machinery that lets you, for example, 
`display` a pict in DrRacket and have an image show up in the 
interactions window. Most ports do not support specials; it doesn't make 
sense for ports that connect to the outside world (file ports, TCP 
ports, etc).


Your original solution using `make-output-port` was probably the right one.

Ryan

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Re: [racket-users] Output Port Shenanigans

[Lehi Toskin]

On Wednesday, March 14, 2018 at 10:10:20 AM UTC-7, Matthew Butterick wrote:
>
>
> probably it requires a combination of peek + read, or copying the port. 
>
> That may be true, but I've been messing around getting *anything* to print 
from inside that function. I'm beginning to think it's never actually being 
run, which leads me to believe this may be a bug. 

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Re: [racket-users] Output Port Shenanigans

[Matthew Butterick]

> On Mar 13, 2018, at 8:50 AM, Lehi Toskin  wrote:
> 
> There must be something I'm missing, but there's not much in the docs that 
> would help me.

Just a guess, but this kind of double-dipping on ports is usually not possible, 
because once bytes are read from a port, they're gone. If you want to display 
the bytes twice, probably it requires a combination of peek + read, or copying 
the port. 

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[racket-users] Output Port Shenanigans

[Lehi Toskin]

Hello, everyone!

I'm trying to get an output port to display text to both the error port and 
a text% object every time there's an error or an `eprintf` is called. Now, 
I have already accomplished this by using `make-output-port`, but I had 
decided to try and use `open-output-text-editor` instead just for gits and 
shiggles. In the procedure documentation it shows that it takes a lambda 
labeled "special filter", so I figured I'd hijack this lambda to then 
fprintf to the error port, but for whatever reason it seems that all 
printing that is done from inside that special filter's scope is sent 

I have tried the following, but without any success:
(define old-out (current-output-port))
; now inside special filter's scope
(lambda (s) (fprintf old-out "foo") s)

There must be something I'm missing, but there's not much in the docs that 
would help me.

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