[Tcl-bugs] [ tcl-Bugs-734402 ] catch fails to catch error

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Bugs item #734402, was opened at 2003-05-07 22:47
Message generated for change (Comment added) made by msofer
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Category: 16. Commands A-H
Group: None
Status: Closed
Resolution: Invalid
Priority: 5
Submitted By: Nobody/Anonymous (nobody)
Assigned to: miguel sofer (msofer)
Summary: catch fails to catch error

Initial Comment:
catch [ error "This is an error"]
   Fails to catch to error in tcl 8.4.2.  In tcl 8.3,
this correctly caught
the error.  For this simple case, the obvious fix is:
catch { error "This is an error" }
However, the difference in behavior affects more
complex scripts.

     -John <jr...@ar...>

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>Comment By: miguel sofer (msofer)
Date: 2003-05-12 17:36

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Ah, but this distinction has nothing to do with the [catch]
command - it is described in the Tcl man page Tcl.n, rule
[2]: when you invoke
   catch [error]
the error occurs during the substitution phase, *before*
[catch] is called (as it is, it never gets called).

Note also that the (buggy) behaviour in 8.3 was inconsistent:

% info patch
8.3.4
% catch [error]
1
% set c catch; $c [error]
wrong # args: should be "error message ?errorInfo? ?errorCode?"




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Comment By: Nobody/Anonymous (nobody)
Date: 2003-05-11 22:01

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  The behavior may be correct, but the man page for "catch"
does not indicate any distinction between "catch [ error ]" and 
"catch { error }".  I believe that, as a minimum, the
documentation of
"catch" should be corrected.

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Comment By: miguel sofer (msofer)
Date: 2003-05-08 09:24

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Doh ... I did have a déjà-vu feeling.

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Comment By: Don Porter (dgp)
Date: 2003-05-08 01:23

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See Bug 219184.  Fixed for Tcl 8.4a3.

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Comment By: miguel sofer (msofer)
Date: 2003-05-07 23:28

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The described 8.4.2 behaviour is correct: 
   catch [ error "This is an error"] 
is semantically equivalent to
   set err [ error "This is an error"] 
   catch $err
as substitution occurs before the [catch] command is 
invoked; as substitution raises an error, [catch] is never 
actually invoked.

Did this really catch the error in 8.3? Could you please post 
the output of
   info patchlevel
in the corresponding interpreter?

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