From Newsgroup: comp.lang.tcl

Hello out there,
I am reviving an old project of mine from around 2008 / 2010 because
I thought I could use some of its parts. The XOTcl version used then
was 1.4 IIRC. The current version is 2.3 which I think is fairly
recent.
My grief is the error message produced when something goes wrong
constructing a new object: The exact reason is - so it seems - never
told - let alone the offending location. This makes it extremely
tedious to advance.
Look at the following example. Context: Having set a particular 'mode'
I click at some place where I want a new line to start. The code:
---
# ctor - coords are <x, y, starting widget>
Line instproc init {canvas coordLst {cName ""}} {
my instvar c cfg coords id

# call base class ctor
lassign $coordLst x y widgets
next $canvas [list $x $y] ;#$cfg ;#$options

set coords {} ; set widgets {}
puts lb
# create first point
my newLinePoint $x $y
puts lc
bindC $c $id <Enter> {s::mkLargePointCurs $c}
}

# Create a new point
Line instproc newLinePoint {x y} {
my instvar c children coords
set x [$c canvasx $x] ; set y [$c canvasy $y]
lappend children [LinePoint [LinePoint autoname Point%d] $c [list
$x $y] \
-parent [self]]
lappend coords $x $y
}
----
I want to create a line starting with a 1st point.
This is the result:
---
Microsoft Windows [Version 10.0.19045.4529]
(c) Microsoft Corporation. Alle Rechte vorbehalten.

d:\x\Test>tclsh main.tcl
lb

and an error window.
---
My conclusions:
- I see 'lb' but not 'lc' - my conclusion is: The error must be in 'newLinePoint'.
- But this is the error message:
--
wrong # args: should be "next canvas coordinates ?mainDict?"
wrong # args: should be "next canvas coordinates ?mainDict?"
::Line ::xotcl::Class->create
invoked from within
"::Line create Line1 .mainFr.c {72 66 ::LEDBtn1} -parent ::C"
("uplevel" body line 1)
invoked from within
"::uplevel $lvl [list [self] create {*}$args]"
(procedure "unknown" line 7)
::Line ::xotcl::Class->unknown
invoked from within
"Line Line$lineNo $c [list $x $y $state] -parent [self]"
(procedure "startCreateLine" line 10)
::C ::Canvas->startCreateLine
invoked from within
"my startCreateLine $state $x $y $line"
...
---
What is this? The call to 'next' has well been passed when it puts out
the 'lb', and in 'newLinePoint' I don't call 'next'.

Questions:
- Has anybody a strategy to cope with this behaviour?
- Or is there a newer version which produces usable error messages?
- I have read that there is a successor to XOTcl.
-- Does it have this same deficiency?
-- If not: Is it somehow upwards compatible with XOTcl?

Oh, this is on Windows 10, 64 bit under tcl 8.6.10.
Any help or idea will be greatly appreciated.
Helmut
PS: Sorry for the long rant.
--- Synchronet 3.20a-Linux NewsLink 1.114

From Newsgroup: comp.lang.tcl

Hi Helmut!

Any help or idea will be greatly appreciated.

I tried to reproduce the erroneous behaviour using XOTcl 2.3 and Tcl
8.6.13 on macOS, but I failed, I am afraid.

Could you create a minimal, reproducible script?

What I tried:

---------------%<---------------
puts [package req Tcl]
puts [package req XOTcl]

## setup

xotcl::Class Base -parameter {parent} \
-instproc init {canvas coordinates {mainDict ""}} {;}

xotcl::Class Line -parameter {{id 321}} -superclass Base

xotcl::Class Point -superclass Base -instproc init {args} {
puts $args
}
xotcl::Class LinePoint -superclass Point
proc ::bindC {args} {;}


## distilled

LinePoint instproc init {canvas {coords ""}} { next }

# ctor - coords are <x, y, starting widget>
Line instproc init {canvas coordLst {cName ""}} {
my instvar c cfg coords id
set c .cc
# call base class ctor
lassign $coordLst x y widgets
set tgt [self next]; puts "$tgt === [[lindex $tgt 0] info instargs [lindex $tgt 2]]"
next $canvas [list $x $y] ;#$cfg ;#$options

set coords {} ; set widgets {}
puts lb
# create first point
my newLinePoint $x $y
puts lc
bindC $c $id <Enter> {s::mkLargePointCurs $c}
}

# Create a new point
Line instproc newLinePoint {x y} {
my instvar c children coords
# set x [$c canvasx $x] ; set y [$c canvasy $y]
lappend children [LinePoint [LinePoint autoname Point%d] $c [list
$x $y] -parent [self]]
lappend coords $x $y
}

## main.tcl ?
::Line Line1 .mainFr.c {72 66 ::LEDBtn1} -parent ::C ---------------%<---------------

This produces:

---------------%<---------------
8.6.13
2.3
::Base instproc init === canvas coordinates mainDict
lb
.cc {72 66}
lc
---------------%<---------------

Could you add the following introspection line just before [next] is
called in your actual script?

---------------%<---------------
set tgt [self next]; puts "$tgt === [[lindex $tgt 0] info instargs
[lindex $tgt 2]]"
---------------%<---------------

Best, Stefan


--- Synchronet 3.20a-Linux NewsLink 1.114

From Newsgroup: comp.lang.tcl

Hi Stefan,
thanks for caring, but I'm afraid I cannot reproduce it any more - the
project has progressed. It turned out that the error message was in
fact correct (it was a call to 'next') but this call wasn't in
'newLinePoint' but in 'LinePoint'.
That's in fact my only grief wth XOTcl: The error message produced
when something goes wrong in a constructor. In other situations the
error message pin points the exact location. I just made a quick test
by 'provoquing' an error. The result was as expected:

Provoqued error
while executing
"error "Provoqued error""
(procedure "checkRelPos" line 3)
::s::Line1 ::s::Line->checkRelPos
invoked from within
"my checkRelPos "
(procedure "straightSegment" line 129)
::s::Line1 ::s::Line->straightSegment
... and so on until
"::s::State2 moveStateHL 435 110 1"
(command bound to event)

Only in a constructor this mechanism apparently doesn't work. Well, I
trust that there is a technical reason for this behaviour and it
cannot be helped.

Apart from that XOTcl is a fantastic tool.
Thanks again, Stefan, and best regards
Helmut
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