try_eval code catch ?finally?

    The  try_eval command evaluates code in the current
    context.

If an error occurs during the evaluation and catch is  not
empty,  then catch is evaluated to handler the error.  The
result of the command, containing the error message,  will
be  stored  in  a global variable errorResult.  The global
variables errorResult, errorInfo  and  errorCode  will  be
imported  into the current scope, there is no need to exe-
cute a global command.  The result of  the  catch  command
becomes  the result of the try_eval command.  If the error
that caused the catch to be evaluate is to  be  continued,
the following command should be used:
error $errorResult $errorCode $errorInfo

If  the  finally argument is supplied and not empty, it is
evaluated after the evaluation of the code and  the  catch
commands.  If an error occurs during the evaluation of the
finally command, it becomes the  result  of  the  try_eval
command.   Otherwise,  the result of either code  or catch
is preserved, as described above.

[TclX] provides '''try_eval'''.