On Sun, Jun 29, 2014 at 05:13:37AM -0700, alab...@yahoo.com wrote:
> 1. I had commented out in desperate hacking attempt to get something in 
> browser!

Sure, but you should be aware that you are mounting the horse from the
rear side ;-)

The Canvas article is NOT a PicoLisp tutorial, and ONLY meant to
demonstrate the use of the Canvas library in PicoLisp.

> 2. There is no /misc/canvas.l file.

Yep! This is only an example in the article. I happen to have it here
locally, in a file "misc/canvas.l" (without a leading slash of course).

> 3. I did try in side the script
> (main go)
> But it didn't work.

This would call the function 'main' with an argument 'go' (i.e. the
value of the symbol 'go').

You could do (main) and then (go).

> 4. Did 
> pil zappel.l -main -go +
> Then it showed red line and changing random numbers. But no running plot.
> 5. Had to fiddle, then figured out by clicking single tab followed by
> step, I could get moving plot.

Here you ran into a situation that we have discussed occasionally in
this group.

You pointed your browser to http://localhost:8080, right?

In short: JavaScript refuses - for security reasons - to post an
XMLHttpRequest if it believes that the destination of the POST is on a
different server ("same origin policy"). For reasons unknown to me, it
does so also if only the port is different, but not the host.

Now, if you connect your browser to port 8080, the session will allocate
a new (ephemeral) port, and use that port subsequently. Thus, JavaScript
refuses to POST initially, and works only later after you clicked
something in the application and thus started a new HTTP transaction.

You don't have this effect, however, if you use 'httpGate' and point
your browser at http://localhost (i.e. the default port 80). Then
httpGate will take care of redirecting to the new port, while the
browser will always use only port 80.

♪♫ Alex
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