From: Ferenc Engard <engard@...>
Date: 2002-08-26T05:05:19+09:00
Subject: Re: interactive ruby/tk app (was: ruby/tk internals)

> You appear to be learning by reading the docs for each part, then seeing
> how to put them together one by one.
> 
> Learn by downloading the ruby tk examples; e-search for
> "ruby-tk81-demos-english", then take one of the (overgrown) examples and
> (painstakingly) remove each bit you don't need. A vaguely OO model will pop
> out.

I have looked for ruby-tk81-demos-english (and other) examples, but
didn't find what I am looking for. I am trying to learn from the source,
but there are things what I cannot figure out.

For example, the following example:

#!/usr/bin/ruby
require "tk"
ctx=binding()
Tk::INTERP._eval("set a blahblah")
eval 'Tk::INTERP._eval("puts $a")',ctx

Returns "blahblah", so it works as I expect.

With the following, I have problems:

-----------------------------
#!/usr/bin/ruby
require "tk"
$topContext=binding()
evalFrame=TkFrame.new { pack }
evalBox=TkText.new(evalFrame) {
    height 10
    pack('fill'=>'x')
}
evalBtn=TkButton.new(evalFrame) {
    text "Execute"
    command proc {evalText(evalBox.value)}
    pack()
}
c=TkCanvas.new {
    background "white"
    pack("fill"=>"both")
}

def evalText(text)
    begin
        puts eval text,$topContext
    rescue Exception => e
      puts "Error running script: #{e}"
    end
end

Tk.mainloop
-----------------------------

This is a test script, for executing ruby code runtime in the top
context, as I have mentioned in my previous post. Try it out, if it is
not clear!

If I evaluate the following text with it:

Tk::INTERP._eval("set a blahblah")
Tk::INTERP._eval("puts $a")

It returns "blahblah" -> Ok.

_BUT_! If I evaluate the two lines step by step (i.e. with two
button-clicks), then I receive this:

blahblah   <-- after 1st click, the value of first eval()

Error running script: c:/ruby/lib/ruby/1.6/tk.rb:971:in `_eval': can't
read "a": no such variable  <-- after 2nd click, a is not defined! :-O

Also, if I execute the string 

Tk::INTERP._eval("puts [info vars]")

It results only one variable, "args", with the value "c0000".

I know the solution is somewhere with the tk package's callback
mechanism, but I cannot figure it out. Could somebody describe it,
please?

Thanks:
Circum