hi,

this is probably already known BUT the "-level" option in "return" does NOT cover the nested loop

the read the following code:

../level-bug.tcl
--------------------------------------
#!/bin/env tclsh

set lvl [lindex $argv 0]

while true {
while true {
puts [info frame $lvl]
return -level $lvl -code break
puts 0
break
}
puts 1
break
} puts 2
------------------------------------

> ./level-bug.tcl 0
type source line 7 file /home/dev1usr/test/level-bug.tcl cmd {info frame $lvl} level 0
1 2

> ./level-bug.tcl 1
type source line 5 file /home/dev1usr/test/level-bug.tcl cmd {while true {
while true {
puts [info frame $lvl]
return -level $lvl -code break
puts 0
break
}
puts 1
break
}} level 0
invoked "break" outside of a loop
while executing
"while true {
while true {
puts [info frame $lvl]
return -level $lvl -code break
puts 0
break
}
puts 1
..."
(file "./level-bug.tcl" line 5)

obvious the while count NOT as level/frame

mfg

aotto1968 <aotto1968@t-online.de> wrote:
> this is probably already known BUT the "-level" option in "return" does NOT cover the nested loop

You're misunderstanding the "-level" of return (even with -code)

The -level was made, so procedures could act like "break", "continue"
or "return" themselves:
proc mybreak {} { return -level 1 -code break } ;# behaves just like "break"

proc myreturnlevel1codebreak {} { return -level 2 -code break }
# ^-- the procedure behaves like "return -level 1 -code break"
proc mybreak2 {} { myreturnlevel1codebreak } ;# again behaves just like "break"

There is no direct way to exit two loops at once, but of course you can do:

proc break3code {} { return 42 } ;# define an arbitrary numeric code once
proc break3 {} { return -code [break3code] } ;# -level 1 is default for return

try {
while true {
while true {
while true {
break3
}
}
}
} on [break3code] {} {};# we broke out of all loops, now continue happily.

Yes, it's a bit awkward, but breaking out of multiple loops isn't all that common.

Andreas Leitgeb <avl@logic.at> wrote:
> aotto1968 <aotto1968@t-online.de> wrote:
>> this is probably already known BUT the "-level" option in "return" does NOT cover the nested loop
> You're misunderstanding the "-level" of return (even with -code)
>
> proc break3code {} { return 42 } ;# define an arbitrary numeric code once
> proc break3 {} { return -code [break3code] } ;# -level 1 is default for return
> try {
> while true {
> while true {
> while true {
> break3
> }
> }
> }
> } on [break3code] {} {};# we broke out of all loops, now continue happily.
>
> Yes, it's a bit awkward, but breaking out of multiple loops isn't all that common.
That example was just to show how it *could* be done with exceptional
exits...

A more common approach instead would rather look like this:

set emergencybreak 0
while true {
while true {
while true {
set emergencybreak 1; break
}
if {$emergencybreak} { break }
}
if {$emergencybreak} { break }
}

On Thursday, May 11, 2023 at 9:50:12 PM UTC+10, Andreas Leitgeb wrote:
> Andreas Leitgeb <a...@logic.at> wrote:
> > aotto1968 <aott...@t-online.de> wrote:
> >> this is probably already known BUT the "-level" option in "return" does NOT cover the nested loop
> > You're misunderstanding the "-level" of return (even with -code)
> >
> > proc break3code {} { return 42 } ;# define an arbitrary numeric code once
> > proc break3 {} { return -code [break3code] } ;# -level 1 is default for return
> > try {
> > while true {
> > while true {
> > while true {
> > break3
> > }
> > }
> > }
> > } on [break3code] {} {};# we broke out of all loops, now continue happily.
> >
> > Yes, it's a bit awkward, but breaking out of multiple loops isn't all that common.
> That example was just to show how it *could* be done with exceptional
> exits...
>
> A more common approach instead would rather look like this:
>
> set emergencybreak 0
> while true {
> while true {
> while true {
> set emergencybreak 1; break
> }
> if {$emergencybreak} { break }
> }
> if {$emergencybreak} { break }
> }

This prompted me to propose support for multi-level break and continue in Jim Tcl.
See:

https://github.com/msteveb/jimtcl/pull/261