The Vocola extension: displaying text and stopping commands early

This extension currently allows displaying text in the "Messages from NatLink" window and stopping processing of a Vocola command sequence, either silently or with an error.

Displaying text

The procedure Vocola.Print(message) displays message in the "Messages from NatLink" window in black. Vocola.Alert(message) is similar but shows message in red.

Stopping commands early

If one of your commands encounters an error, you may wish to immediately stop processing that command (and any following commands in the current command sequence) and display an error. You may do this by calling Vocola.Error(message). This will generate an error message in the "Messages from NatLink" window in red similar to the following:

While executing the following Vocola command:
   'test error'
defined at line 201 of _test_extensions.vcl,
the following error occurred:
   VocolaRuntimeError: your message here

Vocola.Error is an extension function rather than a procedure, so it may be used in value-returning user functions.

Sometimes you may just want to silently stop processing. Vocola.Abort(), an extension procedure, takes care of this. It does not display any messages. One common use of this procedure is to allow user choice in otherwise fixed lists. For example, here is one of my PowerPoint commands:

<shape> := ( shape            = Vocola.Abort()  # user pick
           | line             = {down_2} 
           | arrow            = {down_2}{right} 
           | rectangle        = {down_3} 
           | oval             = {down_4}{right}
           | curved rectangle = {down_3}{right} 
           | left  brace      = {down_7}{right_4}
           | right brace      = {down_7}{right_5}
           );

draw <shape> = Home() sh $1 {enter};

For every choice except "shape", the appropriate shape is selected from the shape menu and created. For "shape", the shape menu is pulled down but then the command is stopped before it can send {enter} to close the menu and create the shape. The user can then send arrow keys followed by enter to choose whatever shape they want from the extensive shape menu.