"uplevel" in "proc" → missing more general "macro"-solution

[aotto1968]

Hi,

an *uplevel-proc* is an *proc* which evaluate the entire content
*uplevel* → example:

proc Format_Return_Error_Check {hdl err} {
uplevel "Format_Error_Check $hdl $err ; set retM void"
}

This simulate a *CPP*-Macro like behavior in *TCL*.

The easy solution to just lice a normal *proc*-body like:

proc Format_Return_Error_Check {hdl err} {
upvar retM retM
Format_Error_Check $hdl $err
set retM void
}

is not really a solution because the "upvar" in a sub-*proc* like
*Format_Error_Check* is broken because *Format_Return_Error_Check*
return an extra call-frame.

solution:

It should be possible to create a *proc* witch *not* add an extra
*level* to the call-frame, a good name would be *macro* :

macro Format_Return_Error_Check {hdl err} {
Format_Error_Check $hdl $err
set retM void
}

The following features should be present:

1) A *macro* argument variable (hdl err) is *only* visible in the macro-body
2) A other variable (retM) is from the calling-call-frame
3) A *macro* deos NOT add a call-frame → an *upvar* in
*Format_Error_Check* should call he calling-call-frame and not the
macro-body-frame

mfg

[heinrichmartin]

On Tuesday, July 19, 2022 at 2:22:08 PM UTC+2, aotto1 wrote:
> Hi,
>
> an *uplevel-proc* is an *proc* which evaluate the entire content
> *uplevel* → example:
>
> proc Format_Return_Error_Check {hdl err} {
> uplevel "Format_Error_Check $hdl $err ; set retM void"
> }
>
> This simulate a *CPP*-Macro like behavior in *TCL*.

Tcl has quite some nice features that can help to prevent duplicate code beyond putting it in a proc. Here are some that are crossing my mind.

1. uplevel

If you stick to your pattern, you are looking for [catch {uplevel 1 {...}} result options], then [dict incr options -level; return {*}$options $result].
You could even write your own proc "macro" that adds this wrapper to the code before actually creating the proc.

2. upvar

As uplevel has a performance penalty (cannot be optimized), upvar'ing well-known or passed variable names should be preferred over uplevel. The catch-wrapper is still needed for generic code.

3. inject code

Sometimes, I am using [proc name args [format {} $inject1 ...]]. I am using it for one-time-setup/config and also to prevent duplicate code.
Pro: Tcl sees a constant proc body and can fully optimize it.
Con: An extra level of escaping, but % is normally not a factor.

4. rewrite code

Just recently, I was injecting a code fix to a foreign proc while initializing my code. This pattern could be extended to rewrite "macros".

apply {{} {
set name this_proc
# build args like for proc
set args [lmap arg [info args $name] {
if {[info default $name $arg default]} {
list $arg $default
} else {
list $arg
}
}]
set body [info body $name]
# re-write to allow $client with parameters
# (braces around proc make my code doc scanner ignore this one)
{proc} $name $args [string map {{invoke $client } {invoke {*}$client }} $body]
log warn "$name was re-written!"
}}

Pro: Tcl sees a constant proc body and can fully optimize it.
Con (for non-Tclers): Might not feel like the natural way of coding ;-)

5. eval

Instead of uplevel, do uplevel without context change: eval.

6. packages/libs

Iirc, there are also a few Tcl packages that hook in to do magic to your code. Others may have names at hand.

HTH
Martin

[Christian Gollwitzer]

Am 20.07.22 um 08:56 schrieb heinrichmartin:

> On Tuesday, July 19, 2022 at 2:22:08 PM UTC+2, aotto1 wrote:

>>
>> This simulate a *CPP*-Macro like behavior in *TCL*.
>

> 6. packages/libs
>
> Iirc, there are also a few Tcl packages that hook in to do magic to your code. Others may have names at hand.
>

Try this: https://wiki.tcl-lang.org/page/Sugar


Christian

[Gerald Lester]

Create a TIP with a sample implementations.



--
+----------------------------------------------------------------------+
| Gerald W. Lester, President, KNG Consulting LLC |
| Email: Gerald...@kng-consulting.net |
+----------------------------------------------------------------------+

[Gerald Lester]

And then there is the Object Orient features.