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INNER {returnImm {Unknow state transition: LINE -> END} {}} CALL {my render_wikit uplevel {http://www.purl.org/tcl/home/man/tcl8.4/TclCmd/uplevel.htm 
[[Hopefully someone will provide some pointers to wiki and other resources relating to uplevel and when one would use it or should '''not''' use it.]]

Harald Kirsch wrote in c.l.t:
''Question: Is it possible to have [[macro]] as a counterpart to [proc] such that [[macro]] defines a "function" which is evaluated in the caller's stack context, i.e. which does not create its own stack context?''

So how's this:
 proc macro {name body} {
        proc $name {} [list uplevel 1 $body]
        set name ;# not needed, but maybe helpful
 } ;# RS
 0 % macro now {incr i; incr j}
 now
 0 % set j 10; set i 1
 1
 0 % now
 11
As a variation, you might also have the body executed in global scope, if you want to avoid [global] commands (not recommended normally, since the variables you use are not cleaned up):
 proc Sub {name body} {
    proc $name {} [list uplevel #0 $body]
 }
 % Sub nenv {array size env}
 % nenv
 44

[DGP] Note that [[macro]] will not be able to handle a 
''body'' that includes a [return] command, due to some
fundamental limitations in Tcl itself.  See tcllib::[control]
documentation for some more details.

[Tcl chatroom] transcript:

suchenwi: I'm not sure what you mean with "will not be able to handle a body that includes a return command". If there is one, it will cause the caller to return, I'd think. And that's like "#define BYE return;" in C - expected behavior for a macro. 

dgp: No, it won't. Try it. 
** Possible `uplevel` deficiencies **
suchenwi: But Harald Kirsch already followed up, he wants 'macro' to take arguments and have local variables. This is tricky indeed - you can't do a "downlevel"... 
[AMG]: Here's a nice, simple [C]-style ''do ... while'' loop implemented using `uplevel`.  Other implementations are available on the [New Control Structures] page.
dgp: Important to remember that [uplevel] adjusts only the command and variable substitution context. It can't really do anything to the calling stack. 
======
suchenwi: Ah - I see. Tried " macro foo {incr i; incr j;return;puts "oops"}". 

dgp: That doesn't test what needs testing 

suchenwi: foo itself returns (the oops won't come), but does not terminate its caller. One would have to do 
 set body [string map {return {return -code return}} $body] ;-) 

 dgp: 
 macro mreturn return 
 proc test {} {puts a; mreturn; puts b} 
 test 

 suchenwi: 
 proc macro {name body} {
    proc $name {} [list uplevel 1 [string map {
             return {return -code return}
    } $body]]} 

dgp: Yes, that string map will handle more cases, but can't achieve [[return -code error]], etc. 
One way to fix this limitation would be to add a new status code to Tcl that caused the result to be evaluated in the caller's context by the caller. 
 return -code eval {set var val} 
Then you would just map all [[return $arg $arg ...]] to
''return -code eval {return $arg $arg ...}'' . Not completely sure what cans of worms get opened by that new feature though.
Of course, with that status code available, [[macro]] would be much easier to write too.

kennykb: I like [[return -code eval]] -- except for deciding whether Tcl_EvalObj and its friends should interpret it or return it to the C caller. 

rmax: Hi Kevin. I think [[return -code eval]] would also help 
[[do]] to become complete for all possible cases. 

kennykb: Yes, dgp's comments make it obvious that it could do return -code eval { return -code eval { return -code whatever {... }}} to break out of multiple scopes. 

dgp: I still would not recommend that though. 
Just as it should always be [[uplevel 1 ...]]. 

kennykb: Don: I wouldn't *recommend* it either, but a certain depth of nesting is needed for [[control::do]] to handle [[return -code]] within the loop body, right? 

rmax: You won't of course create nested [return -code eval] constructs yourself, but they could emerge from nested [do] loops or macro calls. 

 dgp: I think [catch] needs extending too. 
 catch {return -code error foo} msg --> 2 
 set msg --> foo 
But where is the '1' ? 
Add another argument to [catch] to get the '1'. 

kennykb: Yes, also need a place to stash the -errorcode and -errorInfo options to [[return]] 

dgp: I think you can just grab them from ::errorInfo and ::errorCode directly. 

dgp: ...but yes, status code '1' needs special handling, as always, to deal with ::errorInfo and ::errorCode. 
For the rest, set code {catch $body msg} 
 if {$code == 2} { 
 # We caught a return 
D'oh! Make that 
 set code {catch $body msg returncode}
then... 
 return -code eval [list return -code $returncode $msg] 
 } 
dgp: Ah! I think I see what you were getting at! 

kennykb: Hmmmm, it occurs to me that [[return -code eval]] subsumes all the others. 

dgp: If $body itself contains [[return -code eval $script]]. 

kennykb: return -code error -errorcode code -errorinfo into message => return -code eval [[list error message info code]]
 
return -code break => return -code eval break 

kennykb: ... and the same for continue and return. 

suchenwi: Looks like it would actually make the language smaller... 

dgp: ...except maybe for the differences in ::errorInfo construction. 

kennykb: We'd have to keep the other syntax on return for back compatibility, but I think it could simplify the mechanism. 
Oh, yeah, ::errorInfo construction. OK, make it return -code eval [[list error $message [[doTheRightThingWith $info]] $code]]. 

suchenwi: ..and if eval is the last remaining value for -code, one could shorten that to -eval... 

kennykb: Hmm, need a new command for those crazy enough to do [[return -code 6]]. 

dgp: How about "-code ok" ? 
I guess that's the default case where no eval script is done. 
Note: that's different from eval of an empty script. 

Why a new command? 

kennykb: I suppose if you wanted to be obsessive about it, you could say return -code ok $value -> return -code eval [[list identity $value]] where identity is a command that returns its arg, but I wouldn't go that far, myself. 

dgp: We still need [[return -code 6]] if we want ability to create new status codes at the script level. 

rmax: Isn't this possible to handle completely on the [catch] side? Doing it on the [return] side involves string operations on scripts which hurts performance. 

dgp: proc niftyNewBreak {} {return -code 6} 

kennykb: proc niftyNewBreak {} { return -code eval {::tcl::raiseException 6 }} ? 8^) 

rmax: ... and there is the danger of substituting a "return" that isn't really a [return]. 

dgp: Ah, I see. 

kennykb: Where are we doing string operations on scripts? 

dgp: No substitution. catch and re-raise. 

rmax: The implementation of [[do]] would have to substitute "return -code ..." by "return -code eval {return -code ...}" or am I wrong? 

kennykb: Reinhard: Ah, but there's no string processing there. The new command is a pure list. 

dgp: [[do]] includes the line: 
 set code [[catch { uplevel 1 $body } result]]
Change to: 
 set code [catch { uplevel 1 $body } result returnCode] 
Add a case to the [switch]
 2 {return -code eval [list return -code $returnCode $result]} 

kennykb: Yes.. and note that the thing to be 'eval'ed is a pure list. 

dgp: The use of [eval] might prevent bytecode, so that's a performance issue, but there should be no need to reparse the strings. 

rmax: wouldn't "2 {return -code $returnCode $result}"
be sufficient? 

dgp: No. The idea is that the [return] in $body should act as if it was evaluated in the caller. 
Hmmm. so far have taken care of the first pass through [[do]]. 
Remaining passes are handled by an [uplevel 1 {while ...}] 
That probably needs similar handling. Yes. Same changes there. 

rmax: I still think it would be sufficient for [[do]] to be able to catch and pass on the -code argument to return. 

kennykb: Gentleb[[e]]ings, I think we're excising one of the language's major warts here. 

rmax: Can you give an example of usage for [[do]] where that wouldn't be enough? 

* clock : 1011891602 : Jan 24,2002 Thursday 5pm GMT 

kennykb: What if the body of the [[do]] contains [[return -code eval]] ? 

dgp: I think that case is handled above. 

rmax: do will pass on [[return -code eval]]. 

dgp: rmax: you don't want to return from [[do]], you want to return from the caller of [[do]]. 

 rmax: Yes: 
 do { 
    return -code return 
 } 
 inside do: 
 set code [catch { uplevel 1 $body } result retCode] 
 ... 
 2 { return -code [list return $retCode] $result } 
What about that?

dgp: That will return from the caller of [[do]] when what is intended is to return from the caller of the caller of [[do]].
 
* rmax is totally confused now... has to try some things... 

kennykb: That's yet another new syntax for [return]. How is that preferable to "return -code eval [[list return -code $retCode $result]]" ? 

dgp: Oh. I mis-read part of that last one. 
Given what we've described, that should be an error: 

rmax: it is a bit shorter, and I haven't thought much about it... 

dgp: unknown code: "return 2" 

kennykb: Since we need [[return -code eval]] anyway -- in order to implement [[macro]], I'm reluctant to invent still more syntax just to make [[do]] a tiny bit shorter. 

rmax: Yep, Don. It implied another proposal of changing the syntax of [return]. OK, Kevin, you win. 
 
dgp: The numeric code for eval should be -1. 

kennykb: Why -1? 

dgp: #define TCL_EVAL -1 

dgp: It's an interesting status code in that it is completely internal. 
No command will actually return it, it will return the result of eval'ing the result instead. 
[[return -code $integer]] has been documented to allow any postive integer. -1 won't interfere with previous extended status codes. 

kennykb: OK, we have a compatibility issue with C code that calls commandProc's directly. (There are examples doing stuff like that in Brent's book, IIRC). 

dgp: hmmmm... take that back. I guess "positive" isn't in the docs after all. Are there any example doing that with *ObjCmd's ? 

kennykb: I don't think we have too much of a problem as long as we avoid whatever code [[exp_continue]] uses. 

dgp: Any existing code is calling existing command procedures. 
None of which return the status code TCL_EVAL, so is there really a problem? 

bbh: exp_continue seems to be -101 

kennykb: Don: Doesn't Brent's code have a Tcl_GetCommandInfo so that it's actually calling a user-supplied command proc? 

dgp: Anyhow look for a section "Bypassing Tcl_Eval" 

----
See also [namespace], [upvar].
----
[Tcl syntax help] - [Arts and crafts of Tcl-Tk programming]
- [Category Command]} regexp2} CALL {my render uplevel {http://www.purl.org/tcl/home/man/tcl8.4/TclCmd/uplevel.htm 
[[Hopefully someone will provide some pointers to wiki and other resources relating to uplevel and when one would use it or should '''not''' use it.]]

Harald Kirsch wrote in c.l.t:
''Question: Is it possible to have [[macro]] as a counterpart to [proc] such that [[macro]] defines a "function" which is evaluated in the caller's stack context, i.e. which does not create its own stack context?''

So how's this:
 proc macro {name body} {
        proc $name {} [list uplevel 1 $body]
        set name ;# not needed, but maybe helpful
 } ;# RS
 0 % macro now {incr i; incr j}
 now
 0 % set j 10; set i 1
 1
 0 % now
 11
As a variation, you might also have the body executed in global scope, if you want to avoid [global] commands (not recommended normally, since the variables you use are not cleaned up):
 proc Sub {name body} {
    proc $name {} [list uplevel #0 $body]
 }
 % Sub nenv {array size env}
 % nenv
 44

[DGP] Note that [[macro]] will not be able to handle a 
''body'' that includes a [return] command, due to some
fundamental limitations in Tcl itself.  See tcllib::[control]
documentation for some more details.

[Tcl chatroom] transcript:

suchenwi: I'm not sure what you mean with "will not be able to handle a body that includes a return command". If there is one, it will cause the caller to return, I'd think. And that's like "#define BYE return;" in C - expected behavior for a macro. 

dgp: No, it won't. Try it. 
** Possible `uplevel` deficiencies **
suchenwi: But Harald Kirsch already followed up, he wants 'macro' to take arguments and have local variables. This is tricky indeed - you can't do a "downlevel"... 
[AMG]: Here's a nice, simple [C]-style ''do ... while'' loop implemented using `uplevel`.  Other implementations are available on the [New Control Structures] page.
dgp: Important to remember that [uplevel] adjusts only the command and variable substitution context. It can't really do anything to the calling stack. 
======
suchenwi: Ah - I see. Tried " macro foo {incr i; incr j;return;puts "oops"}". 

dgp: That doesn't test what needs testing 

suchenwi: foo itself returns (the oops won't come), but does not terminate its caller. One would have to do 
 set body [string map {return {return -code return}} $body] ;-) 

 dgp: 
 macro mreturn return 
 proc test {} {puts a; mreturn; puts b} 
 test 

 suchenwi: 
 proc macro {name body} {
    proc $name {} [list uplevel 1 [string map {
             return {return -code return}
    } $body]]} 

dgp: Yes, that string map will handle more cases, but can't achieve [[return -code error]], etc. 
One way to fix this limitation would be to add a new status code to Tcl that caused the result to be evaluated in the caller's context by the caller. 
 return -code eval {set var val} 
Then you would just map all [[return $arg $arg ...]] to
''return -code eval {return $arg $arg ...}'' . Not completely sure what cans of worms get opened by that new feature though.
Of course, with that status code available, [[macro]] would be much easier to write too.

kennykb: I like [[return -code eval]] -- except for deciding whether Tcl_EvalObj and its friends should interpret it or return it to the C caller. 

rmax: Hi Kevin. I think [[return -code eval]] would also help 
[[do]] to become complete for all possible cases. 

kennykb: Yes, dgp's comments make it obvious that it could do return -code eval { return -code eval { return -code whatever {... }}} to break out of multiple scopes. 

dgp: I still would not recommend that though. 
Just as it should always be [[uplevel 1 ...]]. 

kennykb: Don: I wouldn't *recommend* it either, but a certain depth of nesting is needed for [[control::do]] to handle [[return -code]] within the loop body, right? 

rmax: You won't of course create nested [return -code eval] constructs yourself, but they could emerge from nested [do] loops or macro calls. 

 dgp: I think [catch] needs extending too. 
 catch {return -code error foo} msg --> 2 
 set msg --> foo 
But where is the '1' ? 
Add another argument to [catch] to get the '1'. 

kennykb: Yes, also need a place to stash the -errorcode and -errorInfo options to [[return]] 

dgp: I think you can just grab them from ::errorInfo and ::errorCode directly. 

dgp: ...but yes, status code '1' needs special handling, as always, to deal with ::errorInfo and ::errorCode. 
For the rest, set code {catch $body msg} 
 if {$code == 2} { 
 # We caught a return 
D'oh! Make that 
 set code {catch $body msg returncode}
then... 
 return -code eval [list return -code $returncode $msg] 
 } 
dgp: Ah! I think I see what you were getting at! 

kennykb: Hmmmm, it occurs to me that [[return -code eval]] subsumes all the others. 

dgp: If $body itself contains [[return -code eval $script]]. 

kennykb: return -code error -errorcode code -errorinfo into message => return -code eval [[list error message info code]]
 
return -code break => return -code eval break 

kennykb: ... and the same for continue and return. 

suchenwi: Looks like it would actually make the language smaller... 

dgp: ...except maybe for the differences in ::errorInfo construction. 

kennykb: We'd have to keep the other syntax on return for back compatibility, but I think it could simplify the mechanism. 
Oh, yeah, ::errorInfo construction. OK, make it return -code eval [[list error $message [[doTheRightThingWith $info]] $code]]. 

suchenwi: ..and if eval is the last remaining value for -code, one could shorten that to -eval... 

kennykb: Hmm, need a new command for those crazy enough to do [[return -code 6]]. 

dgp: How about "-code ok" ? 
I guess that's the default case where no eval script is done. 
Note: that's different from eval of an empty script. 

Why a new command? 

kennykb: I suppose if you wanted to be obsessive about it, you could say return -code ok $value -> return -code eval [[list identity $value]] where identity is a command that returns its arg, but I wouldn't go that far, myself. 

dgp: We still need [[return -code 6]] if we want ability to create new status codes at the script level. 

rmax: Isn't this possible to handle completely on the [catch] side? Doing it on the [return] side involves string operations on scripts which hurts performance. 

dgp: proc niftyNewBreak {} {return -code 6} 

kennykb: proc niftyNewBreak {} { return -code eval {::tcl::raiseException 6 }} ? 8^) 

rmax: ... and there is the danger of substituting a "return" that isn't really a [return]. 

dgp: Ah, I see. 

kennykb: Where are we doing string operations on scripts? 

dgp: No substitution. catch and re-raise. 

rmax: The implementation of [[do]] would have to substitute "return -code ..." by "return -code eval {return -code ...}" or am I wrong? 

kennykb: Reinhard: Ah, but there's no string processing there. The new command is a pure list. 

dgp: [[do]] includes the line: 
 set code [[catch { uplevel 1 $body } result]]
Change to: 
 set code [catch { uplevel 1 $body } result returnCode] 
Add a case to the [switch]
 2 {return -code eval [list return -code $returnCode $result]} 

kennykb: Yes.. and note that the thing to be 'eval'ed is a pure list. 

dgp: The use of [eval] might prevent bytecode, so that's a performance issue, but there should be no need to reparse the strings. 

rmax: wouldn't "2 {return -code $returnCode $result}"
be sufficient? 

dgp: No. The idea is that the [return] in $body should act as if it was evaluated in the caller. 
Hmmm. so far have taken care of the first pass through [[do]]. 
Remaining passes are handled by an [uplevel 1 {while ...}] 
That probably needs similar handling. Yes. Same changes there. 

rmax: I still think it would be sufficient for [[do]] to be able to catch and pass on the -code argument to return. 

kennykb: Gentleb[[e]]ings, I think we're excising one of the language's major warts here. 

rmax: Can you give an example of usage for [[do]] where that wouldn't be enough? 

* clock : 1011891602 : Jan 24,2002 Thursday 5pm GMT 

kennykb: What if the body of the [[do]] contains [[return -code eval]] ? 

dgp: I think that case is handled above. 

rmax: do will pass on [[return -code eval]]. 

dgp: rmax: you don't want to return from [[do]], you want to return from the caller of [[do]]. 

 rmax: Yes: 
 do { 
    return -code return 
 } 
 inside do: 
 set code [catch { uplevel 1 $body } result retCode] 
 ... 
 2 { return -code [list return $retCode] $result } 
What about that?

dgp: That will return from the caller of [[do]] when what is intended is to return from the caller of the caller of [[do]].
 
* rmax is totally confused now... has to try some things... 

kennykb: That's yet another new syntax for [return]. How is that preferable to "return -code eval [[list return -code $retCode $result]]" ? 

dgp: Oh. I mis-read part of that last one. 
Given what we've described, that should be an error: 

rmax: it is a bit shorter, and I haven't thought much about it... 

dgp: unknown code: "return 2" 

kennykb: Since we need [[return -code eval]] anyway -- in order to implement [[macro]], I'm reluctant to invent still more syntax just to make [[do]] a tiny bit shorter. 

rmax: Yep, Don. It implied another proposal of changing the syntax of [return]. OK, Kevin, you win. 
 
dgp: The numeric code for eval should be -1. 

kennykb: Why -1? 

dgp: #define TCL_EVAL -1 

dgp: It's an interesting status code in that it is completely internal. 
No command will actually return it, it will return the result of eval'ing the result instead. 
[[return -code $integer]] has been documented to allow any postive integer. -1 won't interfere with previous extended status codes. 

kennykb: OK, we have a compatibility issue with C code that calls commandProc's directly. (There are examples doing stuff like that in Brent's book, IIRC). 

dgp: hmmmm... take that back. I guess "positive" isn't in the docs after all. Are there any example doing that with *ObjCmd's ? 

kennykb: I don't think we have too much of a problem as long as we avoid whatever code [[exp_continue]] uses. 

dgp: Any existing code is calling existing command procedures. 
None of which return the status code TCL_EVAL, so is there really a problem? 

bbh: exp_continue seems to be -101 

kennykb: Don: Doesn't Brent's code have a Tcl_GetCommandInfo so that it's actually calling a user-supplied command proc? 

dgp: Anyhow look for a section "Bypassing Tcl_Eval" 

----
See also [namespace], [upvar].
----
[Tcl syntax help] - [Arts and crafts of Tcl-Tk programming]
- [Category Command]}} CALL {my revision uplevel} CALL {::oo::Obj1434278 process revision/uplevel} CALL {::oo::Obj1434276 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