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INNER {returnImm {Unknow state transition: LINE -> END} {}} CALL {my render_wikit unset {'''`[http://www.tcl.tk/man/tcl/TclCmd/unset.htm%|%unset]`''', a [Tcl Commands%|%built-in] [Tcl] [command], removes one or more
[variable%|%variables].



** Synopsis **

    :   '''unset''' ?'''-nocomplain'''? ''varName'' ?''varName ...''?



** Documentation **

   [http://www.tcl.tk/man/tcl/TclCmd/unset.htm%|%official reference]:   



** Description **

It is an error for the variables to not already exist, the name to be illegal,
etc. This error can be suppressed with the '''`-nocomplain`''' option.

A [trace] on the variable can resurrect it.

[DKF]: In 8.6, `[unset]` is bytecode compiled. (And don't use `catch
{unset foo}`; the operationally-equivalent `unset -nocomplain foo`
generates much better bytecode.)

----

In retrospect, `unset` should have been designed so that it was not an error to
unset a variable that didn't exist, in which case `-nocomplain` would not have
been necessary.

[aspect]: more support for the above?  I removed it earlier as it's not a sentiment I hear often in the community, and error-by-default seems the appropriate behaviour to me.  Usually (ime) a "no such variable!" error from `unset` identifies a typo I'd rather catch early rather than a spot for `-nocomplain`.

[PYK] 2014-08-15: I added the comment in question after `unset` was mentioned in
[PYK] 2014-08-15: I added comment in question after `unset` was mentioned in
unset and `[glob]` are considered ugly workarounds necessitated by an
unfortunate design decision, and that in general, Tcl commands opt to do less
checking for the sake of more concise scripts, allowing the programmer to add
their own checks where desired.  If error-by-default was the more appropriate
behaviour, the following would raise an error:
behaviour, shouldn't the following raise an error?
======
set x 1
set x 2
======

Leading to:
======


Unsetting a variable will remove all the [trace]s on it.  If there are any `variable unset` traces, they will first be called.

Proc-local variables are implicitly unset when the proc returns.  By using an unset trace, we can do sneaky things:

======
package require lambda 
proc finally {script} {
    set v [lindex [uplevel 1 {info locals}] 0]
    tailcall trace add variable $v unset [lambda args $script]
}

proc test {n cmd} {
    finally {puts "Returning"}
    for {set x 0} {$x < $n} {incr x} {
        puts "$x ... [{*}$cmd]"
    }
}

test 3 {info level}
# 0 ... 1
# 1 ... 1
# 2 ... 1
# Returning
test 3 {expr 1/0}
# Returning
# ERROR: divide by zero
# while evaluating {test 3 {expr 1/0}}
======

** Unset and Tk `-variable` options **

Unsetting a variable that is still bound to an [entry] widget through the `-textvariable` option (for example), strange things may happen (they did in 2002 ...).  Beware if you do this!

Tcl8.6 offers a number of ways to protect against this, which amount to tying the object's lifecycle to the variable.  You can place them both in an object, or use an unset trace on the variable, or interpose a megawidget that binds correctly with [namespace upvar] ...


** Unset and Upvar **

Unsetting an [upvar]-bound variable will also unset all its other bindings (thanks [PYK] for correcting previous text here):

======
set var1 one

proc p1 {} {
    upvar 1 var1 var1 
    unset var1
}

puts [info exists var1] ;# -> 1
p1
puts [info exists var1] ;# -> 0
======

If you want to redirect an upvar binding, you can simply "upvar over the top of it":

======
oo::class create Binder {
    constructor {} {}
    variable var
    method bind {name} {
        upvar 1 $name [self namespace]::var
    }
    method exists {} {
        info exists var
    }
    method get {} {
        set var
    }
    method set {value} {
        set var $value
    }
}


Binder create bee
bee bind foo
puts [bee exists]   ;# -> 0
incr foo 100
puts [bee exists]   ;# -> 1
puts [bee get]      ;# -> 100
bee bind bar
puts [bee exists]   ;# -> 0
set bar check
puts [bee get]      ;# -> check
======

Note that "upvar over the top" will '''not''' work for plain variables (those not created by upvar):

======
Binder create wasp
wasp set bzzzz      ;# this creates the namespace variable without [upvar]
wasp bind foo       ;# ERROR: variable "::oo::Obj16::var" already exists
======    

This has implications for creating objects that mimic Tk's `-variable` (resp. `-textvariable`, `-listvariable`) option.

<<categories>> Tcl syntax | Arts and crafts of Tcl-Tk programming | Command
'''`[http://www.tcl.tk/man/tcl/TclCmd/unset.htm%|%unset]`''', a [Tcl
Commands%|%built-in] [Tcl] [command], removes one or more
[variable%|%variables].



** Synopsis **

    :   '''unset''' ?'''-nocomplain'''? ''varName'' ?''varName ...''?



** Documentation **

   [http://www.tcl.tk/man/tcl/TclCmd/unset.htm%|%official reference]:   



** Description **

It is an error for the variables to not already exist, the name to be illegal,
etc. This error can be suppressed with the '''`-nocomplain`''' option.

A [trace] on the variable can resurrect it.

[DKF]: In 8.6, `[unset]` is bytecode compiled. (And don't use `catch
{unset foo}`; the operationally-equivalent `unset -nocomplain foo`
generates much better bytecode.)

----

In retrospect, `unset` should have been designed so that it was not an error to
unset a variable that didn't exist, in which case `-nocomplain` would not have
been necessary.

[aspect]: more support for the above?  I removed it earlier as it's not a sentiment I hear often in the community, and error-by-default seems the appropriate behaviour to me.  Usually (ime) a "no such variable!" error from `unset` identifies a typo I'd rather catch early rather than a spot for `-nocomplain`.

[PYK] 2014-08-15: I added comment in question after `unset` was mentioned in
the Tcl chatroom on 2014-08-12.  My understanding is that `-nocomplain` for
unset and `[glob]` are considered ugly workarounds necessitated by an
unfortunate design decision, and that in general, Tcl commands opt to do less
checking for the sake of more concise scripts, allowing the programmer to add
their own checks where desired.  If error-by-default was the more appropriate
behaviour, shouldn't the following raise an error?

======
set x 1
set x 2
======



** Unset and Traces **

Unsetting a variable will remove all the [trace]s on it.  If there are any `variable unset` traces, they will first be called.

Proc-local variables are implicitly unset when the proc returns.  By using an unset trace, we can do sneaky things:

======
package require lambda 
proc finally {script} {
    set v [lindex [uplevel 1 {info locals}] 0]
    tailcall trace add variable $v unset [lambda args $script]
}

proc test {n cmd} {
    finally {puts "Returning"}
    for {set x 0} {$x < $n} {incr x} {
        puts "$x ... [{*}$cmd]"
    }
}

test 3 {info level}
# 0 ... 1
# 1 ... 1
# 2 ... 1
# Returning
test 3 {expr 1/0}
# Returning
# ERROR: divide by zero
# while evaluating {test 3 {expr 1/0}}
======

** Unset and Tk `-variable` options **

Unsetting a variable that is still bound to an [entry] widget through the `-textvariable` option (for example), strange things may happen (they did in 2002 ...).  Beware if you do this!

Tcl8.6 offers a number of ways to protect against this, which amount to tying the object's lifecycle to the variable.  You can place them both in an object, or use an unset trace on the variable, or interpose a megawidget that binds correctly with [namespace upvar] ...


** Unset and Upvar **

Unsetting an [upvar]-bound variable will also unset all its other bindings (thanks [PYK] for correcting previous text here):

======
set var1 one

proc p1 {} {
    upvar 1 var1 var1 
    unset var1
}

puts [info exists var1] ;# -> 1
p1
puts [info exists var1] ;# -> 0
======

If you want to redirect an upvar binding, you can simply "upvar over the top of it":

======
oo::class create Binder {
    constructor {} {}
    variable var
    method bind {name} {
        upvar 1 $name [self namespace]::var
    }
    method exists {} {
        info exists var
    }
    method get {} {
        set var
    }
    method set {value} {
        set var $value
    }
}


Binder create bee
bee bind foo
puts [bee exists]   ;# -> 0
incr foo 100
puts [bee exists]   ;# -> 1
puts [bee get]      ;# -> 100
bee bind bar
puts [bee exists]   ;# -> 0
set bar check
puts [bee get]      ;# -> check
======

Note that "upvar over the top" will '''not''' work for plain variables (those not created by upvar):

======
Binder create wasp
wasp set bzzzz      ;# this creates the namespace variable without [upvar]
wasp bind foo       ;# ERROR: variable "::oo::Obj16::var" already exists
======    

This has implications for creating objects that mimic Tk's `-variable` (resp. `-textvariable`, `-listvariable`) option.

<<categories>> Tcl syntax | Arts and crafts of Tcl-Tk programming | Command} regexp2} CALL {my render unset {'''`[http://www.tcl.tk/man/tcl/TclCmd/unset.htm%|%unset]`''', a [Tcl Commands%|%built-in] [Tcl] [command], removes one or more
[variable%|%variables].



** Synopsis **

    :   '''unset''' ?'''-nocomplain'''? ''varName'' ?''varName ...''?



** Documentation **

   [http://www.tcl.tk/man/tcl/TclCmd/unset.htm%|%official reference]:   



** Description **

It is an error for the variables to not already exist, the name to be illegal,
etc. This error can be suppressed with the '''`-nocomplain`''' option.

A [trace] on the variable can resurrect it.

[DKF]: In 8.6, `[unset]` is bytecode compiled. (And don't use `catch
{unset foo}`; the operationally-equivalent `unset -nocomplain foo`
generates much better bytecode.)

----

In retrospect, `unset` should have been designed so that it was not an error to
unset a variable that didn't exist, in which case `-nocomplain` would not have
been necessary.

[aspect]: more support for the above?  I removed it earlier as it's not a sentiment I hear often in the community, and error-by-default seems the appropriate behaviour to me.  Usually (ime) a "no such variable!" error from `unset` identifies a typo I'd rather catch early rather than a spot for `-nocomplain`.

[PYK] 2014-08-15: I added the comment in question after `unset` was mentioned in
[PYK] 2014-08-15: I added comment in question after `unset` was mentioned in
unset and `[glob]` are considered ugly workarounds necessitated by an
unfortunate design decision, and that in general, Tcl commands opt to do less
checking for the sake of more concise scripts, allowing the programmer to add
their own checks where desired.  If error-by-default was the more appropriate
behaviour, the following would raise an error:
behaviour, shouldn't the following raise an error?
======
set x 1
set x 2
======

Leading to:
======


Unsetting a variable will remove all the [trace]s on it.  If there are any `variable unset` traces, they will first be called.

Proc-local variables are implicitly unset when the proc returns.  By using an unset trace, we can do sneaky things:

======
package require lambda 
proc finally {script} {
    set v [lindex [uplevel 1 {info locals}] 0]
    tailcall trace add variable $v unset [lambda args $script]
}

proc test {n cmd} {
    finally {puts "Returning"}
    for {set x 0} {$x < $n} {incr x} {
        puts "$x ... [{*}$cmd]"
    }
}

test 3 {info level}
# 0 ... 1
# 1 ... 1
# 2 ... 1
# Returning
test 3 {expr 1/0}
# Returning
# ERROR: divide by zero
# while evaluating {test 3 {expr 1/0}}
======

** Unset and Tk `-variable` options **

Unsetting a variable that is still bound to an [entry] widget through the `-textvariable` option (for example), strange things may happen (they did in 2002 ...).  Beware if you do this!

Tcl8.6 offers a number of ways to protect against this, which amount to tying the object's lifecycle to the variable.  You can place them both in an object, or use an unset trace on the variable, or interpose a megawidget that binds correctly with [namespace upvar] ...


** Unset and Upvar **

Unsetting an [upvar]-bound variable will also unset all its other bindings (thanks [PYK] for correcting previous text here):

======
set var1 one

proc p1 {} {
    upvar 1 var1 var1 
    unset var1
}

puts [info exists var1] ;# -> 1
p1
puts [info exists var1] ;# -> 0
======

If you want to redirect an upvar binding, you can simply "upvar over the top of it":

======
oo::class create Binder {
    constructor {} {}
    variable var
    method bind {name} {
        upvar 1 $name [self namespace]::var
    }
    method exists {} {
        info exists var
    }
    method get {} {
        set var
    }
    method set {value} {
        set var $value
    }
}


Binder create bee
bee bind foo
puts [bee exists]   ;# -> 0
incr foo 100
puts [bee exists]   ;# -> 1
puts [bee get]      ;# -> 100
bee bind bar
puts [bee exists]   ;# -> 0
set bar check
puts [bee get]      ;# -> check
======

Note that "upvar over the top" will '''not''' work for plain variables (those not created by upvar):

======
Binder create wasp
wasp set bzzzz      ;# this creates the namespace variable without [upvar]
wasp bind foo       ;# ERROR: variable "::oo::Obj16::var" already exists
======    

This has implications for creating objects that mimic Tk's `-variable` (resp. `-textvariable`, `-listvariable`) option.

<<categories>> Tcl syntax | Arts and crafts of Tcl-Tk programming | Command
'''`[http://www.tcl.tk/man/tcl/TclCmd/unset.htm%|%unset]`''', a [Tcl
Commands%|%built-in] [Tcl] [command], removes one or more
[variable%|%variables].



** Synopsis **

    :   '''unset''' ?'''-nocomplain'''? ''varName'' ?''varName ...''?



** Documentation **

   [http://www.tcl.tk/man/tcl/TclCmd/unset.htm%|%official reference]:   



** Description **

It is an error for the variables to not already exist, the name to be illegal,
etc. This error can be suppressed with the '''`-nocomplain`''' option.

A [trace] on the variable can resurrect it.

[DKF]: In 8.6, `[unset]` is bytecode compiled. (And don't use `catch
{unset foo}`; the operationally-equivalent `unset -nocomplain foo`
generates much better bytecode.)

----

In retrospect, `unset` should have been designed so that it was not an error to
unset a variable that didn't exist, in which case `-nocomplain` would not have
been necessary.

[aspect]: more support for the above?  I removed it earlier as it's not a sentiment I hear often in the community, and error-by-default seems the appropriate behaviour to me.  Usually (ime) a "no such variable!" error from `unset` identifies a typo I'd rather catch early rather than a spot for `-nocomplain`.

[PYK] 2014-08-15: I added comment in question after `unset` was mentioned in
the Tcl chatroom on 2014-08-12.  My understanding is that `-nocomplain` for
unset and `[glob]` are considered ugly workarounds necessitated by an
unfortunate design decision, and that in general, Tcl commands opt to do less
checking for the sake of more concise scripts, allowing the programmer to add
their own checks where desired.  If error-by-default was the more appropriate
behaviour, shouldn't the following raise an error?

======
set x 1
set x 2
======



** Unset and Traces **

Unsetting a variable will remove all the [trace]s on it.  If there are any `variable unset` traces, they will first be called.

Proc-local variables are implicitly unset when the proc returns.  By using an unset trace, we can do sneaky things:

======
package require lambda 
proc finally {script} {
    set v [lindex [uplevel 1 {info locals}] 0]
    tailcall trace add variable $v unset [lambda args $script]
}

proc test {n cmd} {
    finally {puts "Returning"}
    for {set x 0} {$x < $n} {incr x} {
        puts "$x ... [{*}$cmd]"
    }
}

test 3 {info level}
# 0 ... 1
# 1 ... 1
# 2 ... 1
# Returning
test 3 {expr 1/0}
# Returning
# ERROR: divide by zero
# while evaluating {test 3 {expr 1/0}}
======

** Unset and Tk `-variable` options **

Unsetting a variable that is still bound to an [entry] widget through the `-textvariable` option (for example), strange things may happen (they did in 2002 ...).  Beware if you do this!

Tcl8.6 offers a number of ways to protect against this, which amount to tying the object's lifecycle to the variable.  You can place them both in an object, or use an unset trace on the variable, or interpose a megawidget that binds correctly with [namespace upvar] ...


** Unset and Upvar **

Unsetting an [upvar]-bound variable will also unset all its other bindings (thanks [PYK] for correcting previous text here):

======
set var1 one

proc p1 {} {
    upvar 1 var1 var1 
    unset var1
}

puts [info exists var1] ;# -> 1
p1
puts [info exists var1] ;# -> 0
======

If you want to redirect an upvar binding, you can simply "upvar over the top of it":

======
oo::class create Binder {
    constructor {} {}
    variable var
    method bind {name} {
        upvar 1 $name [self namespace]::var
    }
    method exists {} {
        info exists var
    }
    method get {} {
        set var
    }
    method set {value} {
        set var $value
    }
}


Binder create bee
bee bind foo
puts [bee exists]   ;# -> 0
incr foo 100
puts [bee exists]   ;# -> 1
puts [bee get]      ;# -> 100
bee bind bar
puts [bee exists]   ;# -> 0
set bar check
puts [bee get]      ;# -> check
======

Note that "upvar over the top" will '''not''' work for plain variables (those not created by upvar):

======
Binder create wasp
wasp set bzzzz      ;# this creates the namespace variable without [upvar]
wasp bind foo       ;# ERROR: variable "::oo::Obj16::var" already exists
======    

This has implications for creating objects that mimic Tk's `-variable` (resp. `-textvariable`, `-listvariable`) option.

<<categories>> Tcl syntax | Arts and crafts of Tcl-Tk programming | Command}} CALL {my revision unset} CALL {::oo::Obj157126 process revision/unset} CALL {::oo::Obj157124 process}

-errorcode

NONE

-errorinfo

Unknow state transition: LINE -> END
    while executing
"error $msg"
    (class "::Wiki" method "render_wikit" line 6)
    invoked from within
"my render_$default_markup $N $C $mkup_rendering_engine"
    (class "::Wiki" method "render" line 8)
    invoked from within
"my render $name $C"
    (class "::Wiki" method "revision" line 31)
    invoked from within
"my revision $page"
    (class "::Wiki" method "process" line 56)
    invoked from within
"$server process [string trim $uri /]"

-errorline

4