[Tcl-bugs] [ tcl-Bugs-2134049 ] info frame documentation error

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Bugs item #2134049, was opened at 2008-09-28 13:11
Message generated for change (Settings changed) made by dkf
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Category: 17. Commands I-L
Group: current: 8.5.4
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Lars Hellstrm (lars_h)
>Assigned to: Andreas Kupries (andreas_kupries)
Summary: info frame documentation error

Initial Comment:
The description of what [info frame] does when given a positive level argument is as follows:

  If number is positive (> 0) then it selects a particular 
  stack level (1 refers to the top-most active command, 
  i.e., info frame itself, 2 to the command it was called 
  from, and so on)

However, [info frame] is in practice almost never the top-most active command, so this is wrong. Defining

proc nest {levels} {
  if {$levels<1} then {
    for {set n 1} {$n<=[info frame]} {incr n} {
      puts [format {%d: %s} $n [info frame $n]]
    }
  } else {
    nest [incr levels -1]
  }
}

one gets

% nest 3
1: type eval line 1 cmd {nest 3} level 4
2: type proc line 7 cmd {nest [incr levels -1]} proc ::nest level 3
3: type proc line 7 cmd {nest [incr levels -1]} proc ::nest level 2
4: type proc line 7 cmd {nest [incr levels -1]} proc ::nest level 1
5: type proc line 4 cmd {info frame $n} proc ::nest level 0

i.e., it is [info frame [info frame]] that selects the info frame call itself.

Also wrong is the claim that [info frame 2] provides information about the command from which [dict get [info frame 1] cmd] was called, since the above shows it is really the other way around: [dict get [info frame 1] cmd] caused [dict get [info frame 2] cmd] to be called.

The corresponding sentence in the description of [info level] describes these relationships correctly:

  If number is positive then it selects a particular stack level 
  (1 refers to the top-most active procedure, 2 to the 
  procedure it called, and so on);

Possibly it is the use of "top-most" that confuses the issue (does the stack grow top to bottom or bottom to top?), so maybe it would be a good idea to replace this term by "outermost".

An alternative wording is:

  If number is positive then it selects a particular 
  stack level (1 refers to the outermost active procedure, 
  2 to the procedure it called, and so on, up to the current 
  frame level which refers to the info frame itself);



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