Am 24.06.2025 um 10:23 schrieb Mark Summerfield:

I have a switch command which is doing something I don't expect but I
don't understand what I've done wrong. In this example the default is
always executed but I expect the case before that to be executed.

const UNCOMPRESSED U
const ZLIB_COMPRESSED Z
const SAME_AS_PREV =
set filename somefile.txt
set action "added"
set kind Z
switch $kind {
$::SAME_AS_PREV { puts "unchanged \"$filename\"" }
$::UNCOMPRESSED { puts "$action \"$filename\"" }
$::ZLIB_COMPRESSED { puts "$action \"$filename\" (zlib
compressed)" }
default { puts "!!!!!!!! UNEXPECTED !!!!!!!!" }
}

What am I doing wrong?

Nothing wrong. Tcl is just different, sorry for that.

The "{" always avoids expansion of variables and commands. If you want
to use variables in the switch, you have to avoid the "{".

switch -exact -- $kind [list\
$::SAME_AS_PREV { puts "unchanged \"$filename\"" }\
$::UNCOMPRESSED { puts "$action \"$filename\"" }
$::ZLIB_COMPRESSED { puts "$action \"$filename\" (zlib
compressed)" }\
default { puts "!!!!!!!! UNEXPECTED !!!!!!!!" }\
]

Nevertheless, this is no fun on the quoting level (backslashes at the
end etc). In addition, you have to take care, when the variable
expansion happens. This might be tricky.

I personally would write it like that:

switch -exact -- $kind {
= { # SAME_AS_PREV
puts "unchanged \"$filename\""
}
U { # UNCOMPRESSED
puts "$action \"$filename\""
}
Z { # ZLIB_COMPRESSED
puts "$action \"$filename\" (zlib compressed)"
}
default { puts "!!!!!!!! UNEXPECTED !!!!!!!!" }
}

Harald

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Am 24.06.2025 um 10:46 schrieb Mark Summerfield:

On Tue, 24 Jun 2025 10:37:08 +0200, Harald Oehlmann wrote:

Am 24.06.2025 um 10:23 schrieb Mark Summerfield:

I have a switch command which is doing something I don't expect but I
don't understand what I've done wrong. In this example the default is
always executed but I expect the case before that to be executed.

const UNCOMPRESSED U const ZLIB_COMPRESSED Z const SAME_AS_PREV =
set filename somefile.txt set action "added"
set kind Z switch $kind {
$::SAME_AS_PREV { puts "unchanged \"$filename\"" }
$::UNCOMPRESSED { puts "$action \"$filename\"" }
$::ZLIB_COMPRESSED { puts "$action \"$filename\" (zlib
compressed)" }
default { puts "!!!!!!!! UNEXPECTED !!!!!!!!" }
}

What am I doing wrong?

Nothing wrong. Tcl is just different, sorry for that.

The "{" always avoids expansion of variables and commands. If you want
to use variables in the switch, you have to avoid the "{".

switch -exact -- $kind [list\
$::SAME_AS_PREV { puts "unchanged \"$filename\"" }\
$::UNCOMPRESSED { puts "$action \"$filename\"" }
$::ZLIB_COMPRESSED { puts "$action \"$filename\" (zlib
compressed)" }\
default { puts "!!!!!!!! UNEXPECTED !!!!!!!!" }\
]

Nevertheless, this is no fun on the quoting level (backslashes at the
end etc). In addition, you have to take care, when the variable
expansion happens. This might be tricky.

I personally would write it like that:

switch -exact -- $kind {
= { # SAME_AS_PREV
puts "unchanged \"$filename\""
}
U { # UNCOMPRESSED
puts "$action \"$filename\""
}
Z { # ZLIB_COMPRESSED
puts "$action \"$filename\" (zlib compressed)"
}
default { puts "!!!!!!!! UNEXPECTED !!!!!!!!" }
}

Harald

Thanks that works great.

Bit of a disinsentive to use consts though!

Great, that it works for you.

If I want to compare something with multiple variables, I would use an
if chain:

if {$kind eq $::SAME_AS_PREV} {
puts "unchanged \"$filename\""
} else if {$kind eq $::UNCOMPRESSED} {
puts "$action \"$filename\""
} else if {$kind eq $::ZLIB_COMPRESSED} {
puts "$action \"$filename\" (zlib >> compressed)"
} else {
puts "!!!!!!!! UNEXPECTED !!!!!!!!"
}

The "if" command takes his first argument and passes it to "expr".
Then, eval will do the variable expansion.
This does not happen with "switch".

I never used const. But its use may help for clarity.

Harald

--- SoupGate-Win32 v1.05
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Sorry, typo in my last post:

The "if" command takes his first argument and passes it to "expr".
Then, eval will do the variable expansion.

Correct:

Then, expr will do the variable expansion.

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 24/06/2025 10:23, Mark Summerfield wrote:

I have a switch command which is doing something I don't expect but I
don't understand what I've done wrong. In this example the default is
always executed but I expect the case before that to be executed.

const UNCOMPRESSED U
const ZLIB_COMPRESSED Z
const SAME_AS_PREV =
set filename somefile.txt
set action "added"
set kind Z
switch $kind {
$::SAME_AS_PREV { puts "unchanged \"$filename\"" }
$::UNCOMPRESSED { puts "$action \"$filename\"" }
$::ZLIB_COMPRESSED { puts "$action \"$filename\" (zlib
compressed)" }
default { puts "!!!!!!!! UNEXPECTED !!!!!!!!" }
}

What am I doing wrong?

Switch allows for two different ways to specify the pattern/body pairs:
As as a single argument or as individual arguments. If you want the
patterns to be in variables (or consts) you may prefer the latter
method. This can be written as:

switch $kind \
$::SAME_AS_PREV {
puts "unchanged \"$filename\""
} $::UNCOMPRESSED {
puts "$action \"$filename\""
} $::ZLIB_COMPRESSED {
puts "$action \"$filename\" (zlib compressed)"
} default {
puts "!!!!!!!! UNEXPECTED !!!!!!!!"
}


Schelte.

--- SoupGate-Win32 v1.05
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Am 24.06.2025 um 12:53 schrieb Schelte:

On 24/06/2025 10:23, Mark Summerfield wrote:

I have a switch command which is doing something I don't expect but I
don't understand what I've done wrong. In this example the default is
always executed but I expect the case before that to be executed.

     const UNCOMPRESSED U
     const ZLIB_COMPRESSED Z
     const SAME_AS_PREV =
     set filename somefile.txt
     set action "added"
     set kind Z
     switch $kind {
         $::SAME_AS_PREV { puts "unchanged \"$filename\"" }
         $::UNCOMPRESSED { puts "$action \"$filename\"" }
         $::ZLIB_COMPRESSED { puts "$action \"$filename\" (zlib
compressed)" }
         default { puts "!!!!!!!! UNEXPECTED !!!!!!!!" }
     }

What am I doing wrong?

Switch allows for two different ways to specify the pattern/body pairs:
As as a single argument or as individual arguments. If you want the
patterns to be in variables (or consts) you may prefer the latter
method. This can be written as:

switch $kind \
  $::SAME_AS_PREV {
    puts "unchanged \"$filename\""
} $::UNCOMPRESSED {
    puts "$action \"$filename\""
} $::ZLIB_COMPRESSED {
    puts "$action \"$filename\" (zlib compressed)"
} default {
    puts "!!!!!!!! UNEXPECTED !!!!!!!!"
}

Schelte.

RIGHT YOU ARE !

--- SoupGate-Win32 v1.05
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At Tue, 24 Jun 2025 08:46:57 -0000 (UTC) Mark Summerfield <[email protected]> wrote:

On Tue, 24 Jun 2025 10:37:08 +0200, Harald Oehlmann wrote:

Am 24.06.2025 um 10:23 schrieb Mark Summerfield:

I have a switch command which is doing something I don't expect but I
don't understand what I've done wrong. In this example the default is
always executed but I expect the case before that to be executed.

const UNCOMPRESSED U const ZLIB_COMPRESSED Z const SAME_AS_PREV > >> set filename somefile.txt set action "added"
set kind Z switch $kind {
$::SAME_AS_PREV { puts "unchanged \"$filename\"" }
$::UNCOMPRESSED { puts "$action \"$filename\"" }
$::ZLIB_COMPRESSED { puts "$action \"$filename\" (zlib
compressed)" }
default { puts "!!!!!!!! UNEXPECTED !!!!!!!!" }
}

What am I doing wrong?

Nothing wrong. Tcl is just different, sorry for that.

The "{" always avoids expansion of variables and commands. If you want
to use variables in the switch, you have to avoid the "{".

switch -exact -- $kind [list\
$::SAME_AS_PREV { puts "unchanged \"$filename\"" }\
$::UNCOMPRESSED { puts "$action \"$filename\"" }
$::ZLIB_COMPRESSED { puts "$action \"$filename\" (zlib compressed)" }\
default { puts "!!!!!!!! UNEXPECTED !!!!!!!!" }\
]

Nevertheless, this is no fun on the quoting level (backslashes at the
end etc). In addition, you have to take care, when the variable
expansion happens. This might be tricky.

I personally would write it like that:

switch -exact -- $kind {
= { # SAME_AS_PREV
puts "unchanged \"$filename\""
}
U { # UNCOMPRESSED
puts "$action \"$filename\""
}
Z { # ZLIB_COMPRESSED
puts "$action \"$filename\" (zlib compressed)"
}
default { puts "!!!!!!!! UNEXPECTED !!!!!!!!" }
}

Harald

Thanks that works great.

Bit of a disinsentive to use consts though!

Yes. You really can't use them the way you do in C/C++. Tcl does not really have "const". It also really does not have "statements". Tcl is like LISP in many ways.




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