TCL/tk problem in Shen/tk graphics

[dr.mt...@gmail.com]

I used to keep this stuff off this group, but since the main TCL/tk group has been killed,

there's no obvious group to go to.  Somebody with enough TCL/tk knowledge might be able to solve this one.

This program reads a TCL/tk command from a file.  For example:

button .b eot

The eot (end of transmission) shows the command is ready to be executed.   The function newcommand? tests the file for a new command

proc newcommand? {File} {
  set Source [open $File r]
  set Data [read $Source]
  set Verdict [eot? $Data]
  close $Source
  return $Verdict}

proc eot? {S} {
   return [ string match *eot $S ]
   } 

So I put  button .b eot  into the file which is called in in the program.  I ask TCL if there is a new command waiting.

(bin) 23 % newcommand? $in
1

TCL/tk says yes.  I then tell TCL to enact what is in this file.

proc enact {File} {
  set Source [open $File r]
  set Data [read $Source]
  set Command [trim $Data]
  overwrite $File
  eval $Command
  close $Source}

trim just trims the eot off the file contents.  So I enter enact $in.  The contents are eaten and the in file is now empty.  If I then submit

pack .b eot

in the same way; sure enough the button appears in WISH.  Now I enter

set myvar 1

and enact that.   But if I then enter 

puts $myvar

I get 

can't read "myvar": no such variable

Mark

[Mark Tarver]

Slightly better is to close the first stream before overwriting the file

proc enact {File} {
  set Source [open $File r]
  set Data [read $Source]

  close $Source

  set Command [trim $Data]

  overwrite $File
  eval $Command
  }

proc overwrite {File} {
  set Sink [open $File w]
  puts -nonewline $Sink ""
  flush $Sink
  close $Sink}

However it has no effect on the problem.

Mark

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[Bruno Deferrari]

It is not clear to me where you are calling "set myvar", is that code that would be processed by the eval call?

It is probably being evaluated in a different environment than the "puts $myvar" you have later.

I found https://www.tcl-lang.org/man/tcl8.6/TclCmd/global.htm, so after the `set myvar` (or maybe before) you could try "global myvar"

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--

BD

[Bruno Deferrari]

This may be useful too (to avoid the global scope and run your evals in a controlled context):

 https://www.tcl-lang.org/man/tcl8.6/TclCmd/namespace.htm

--

BD

[Mark Tarver]

Yes; I was just going out of the door and it hit me before 

I read your post.  The set myvar is being read locally

and probably the variable only exists within the enact

procedure.   It;s a bit of an odd case because the 

variable isn't cited in the procedure itself but TCL/tk has

decided to make it local.

There's probably a command to force variables to be global

but right now the sun is shining and I'm out.

Mark

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[Bruno Deferrari]

Btw, as an alternative to the mailing lists, you can try those AI chatbots, they are usually quite good at answering programming questions. Free versions are usually limited in time or amount of queries, but that is usually more than good enough for cases like this.

Not sure which one is the best these days, but a few I have tried are:

https://claude.ai/chats

https://chat.openai.com/

https://groq.com/

and on this page you can try two models at the same time to compare the answers:

https://arena.lmsys.org/

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BD

[dr.mt...@gmail.com]

Thanks.  TCL/tk seems to resist

using the global declaration in this 

context because the variables are

dynamically generated.  This only

affects one feature of Shen/tk which

is the ability to call down web pages.  

There is a workaround for this I think

which might work.

M.

[dr.mt...@gmail.com]

I still have a technical TCL/tk problem here and its gone to Stackoverflow.

https://stackoverflow.com/questions/78476359/downloading-a-web-page-using-tcl-tk

for those who might have an answer.

Mark