[ltk-user] How is ":serve-event t" meant to be used?

[edgar]

Hi all on the LTK list,

I'm trying to open a scrolled-canvas widget in the Tk main window and
then interactively drawing a line on the canvas (details in the REPL
transcripts below), but LTK is throwing nothing but errors at me.

The questions are:

1. Am I doing something fundamentally wrong in the examples below?

2. In case the errors are based on bugs in LTK, how can I help to
   improve the situation?

I have some experience in both Tcl/Tk and Common Lisp. I'm a hardware
electrician and not a professional programmer, but I know how to use
diff to produce patches. But before starting to hack around in the
LTK code I would first like to hear an opinion of somebody who has
better insight than me into the LTK internals.

SBCL 1.1.12 on Debian 7.2 Wheezy (64-bit), LTK 0.98, Tcl/Tk 8.5

Here is what I'm doing:

------------------------- Start of REPL Transcript ---------------------

CL-USER> (ql:quickload :ltk)
; Loading "ltk"
(:LTK)

CL-USER> ltk:*ltk-version*
"0.98"

CL-USER> (defpackage :ltk-test (:use :cl :ltk))
#<PACKAGE "LTK-TEST">

CL-USER> (in-package :ltk-test)
#<PACKAGE "LTK-TEST">

LTK-TEST> (defparameter *canvas* nil)
*CANVAS*

LTK-TEST> (defun ltk-test ()
            (with-ltk (:serve-event t)
              (let ((sc (make-instance 'scrolled-canvas)))
                    (pack sc :expand 1 :fill :both)
                    (setf *canvas* (canvas sc)))))
LTK-TEST

LTK-TEST> (ltk-test)
; the Tk window appears on the screen
NIL

LTK-TEST> (create-line *canvas* '(10 10 20 20))

The value NIL is not of type STREAM.
   [Condition of type TYPE-ERROR]

Backtrace:
  0: (LTK::FLUSH-WISH)
  1: (CREATE-LINE #<CANVAS {1004C0DC13}> (10 10 20 20))
  2: (SB-INT:SIMPLE-EVAL-IN-LEXENV
       (CREATE-LINE *CANVAS* (QUOTE (10 10 20 20))) #<NULL-LEXENV>)
  3: (EVAL (CREATE-LINE *CANVAS* (QUOTE (10 10 20 20))))

;; Looking at the definition of FLUSH-WISH in ltk.lisp, the reason
;; for the error seems to be: (wish-stream *wish*) => NIL

LTK-TEST> *wish*
#S(LTK::LTK-CONNECTION
   :STREAM NIL
   :CALLBACKS #<HASH-TABLE :TEST EQUAL :COUNT 0 {1007C0E9D3}>
   :AFTER-IDS #<HASH-TABLE :TEST EQUAL :COUNT 0 {1007C0EA73}>
   :COUNTER 1
   :AFTER-COUNTER 1
   :EVENT-QUEUE NIL
   :CALL-WITH-CONDITION-HANDLERS-FUNCTION
     #<FUNCTION (LAMBDA # :IN MAKE-LTK-CONNECTION) {1007C0EDCB}>
   :INPUT-HANDLER NIL
   :REMOTEP NIL
   :OUTPUT-BUFFER ("senddata [.wc.wf create line  10 10 20 20]")
   :VARIABLES #<HASH-TABLE :TEST EQUAL :COUNT 0 {1007C0EE53}>)

-------------------------- End of REPL Transcript ----------------------

Here is what happens if I try to do the same thing manually:

------------------------- Start of REPL Transcript ---------------------

LTK-TEST> (start-wish)
; an empty Tk window appears on the screen
NIL

LTK-TEST> (mainloop :serve-event t)
NIL

LTK-TEST> (defparameter *scrolled-canvas* (make-instance
'scrolled-canvas)) *SCROLLED-CANVAS*

LTK-TEST> (pack *scrolled-canvas* :expand 1 :fill :both)
; the scrolled-canvas widget appears in the Tk window
#<SCROLLED-CANVAS {10040DEB83}>

LTK-TEST> (defparameter *canvas* (canvas *scrolled-canvas*))
*CANVAS*

LTK-TEST> (create-line *canvas* '(10 10 20 20))
; YIPPIE, a line appears on the canvas :-)
1

LTK-TEST> (setf *exit-mainloop* t)
; the Tk window doesn't disappear from the screen
T

LTK-TEST> (exit-wish)
attempt to THROW to a tag that does not exist:
 #S(LTK::LTK-CONNECTION
    :STREAM NIL
    :CALLBACKS #<HASH-TABLE :TEST EQUAL :COUNT 0 {10068F9063}>
    :AFTER-IDS #<HASH-TABLE :TEST EQUAL :COUNT 0 {10068F9103}>
    :COUNTER 5
    :AFTER-COUNTER 1
    :EVENT-QUEUE NIL
    :CALL-WITH-CONDITION-HANDLERS-FUNCTION #<FUNCTION FUNCALL>
    :INPUT-HANDLER NIL
    :REMOTEP NIL
    :OUTPUT-BUFFER NIL
    :VARIABLES #<HASH-TABLE
    :TEST EQUAL :COUNT 0 {10068F91A3}>)
   [Condition of type SB-INT:SIMPLE-CONTROL-ERROR]

Backtrace:
  0: ("no debug information for frame")
  1: (EXIT-WISH) [tl,external]
  2: (SB-INT:SIMPLE-EVAL-IN-LEXENV (EXIT-WISH) #<NULL-LEXENV>)
  3: (EVAL (EXIT-WISH))

-------------------------- End of REPL Transcript ----------------------

Looking at the definition of EXIT-WISH in ltk.lisp, the reason for
the error is the line (throw *wish* nil) but I'm not sure if the
EXIT-WISH function is meant to be called in this context at all.

The question remains:

How is ":serve-event t" meant to be used in a meaningful way?

Or am I too stupid to use LTK properly?

Thanks in advance for your answers,

- edgar