try_eval code catch ?finally?

          The try_eval command evaluates code in the current con-
          text.

     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 vari-
     ables errorResult, errorInfo and errorCode will be  imported
     into the current scope, there is no need to execute 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 com-
     mand.  Otherwise, the result of either  code   or  catch  is
     preserved, as described above.

     This command is provided by Extended Tcl.