How to make festival evaulate its own scheme expressions from the command line, so as to change voices as needed?

I can't seem to find any documentation on this. This forum post shows someone trying to change the voice used by festival, outside of the festival interpreter, using a command-line flag. festival --\(voice_kal_diphone\) --tts "Langalist.txt" It doesn't work. As a solution, the OP's program's configuration file ends up being edited. Everyone here also seems to use that method to select voices. But surely, if from within the program's scheme interpreter the expression luisetta@riverbrain:~$ festival Festival Speech Synthesis System 2.1:release November 2010 Copyright (C) University of Edinburgh, 1996-2010. All rights reserved. clunits: Copyright (C) University of Edinburgh and CMU 1997-2010 hts_engine: The HMM-based speech synthesis system (HTS) hts_engine API version 1.04 (http://hts-engine.sourceforge.net/) Copyright (C) 2001-2010 Nagoya Institute of Technology 2001-2008 Tokyo Institute of Technology All rights reserved. For details type `(festival_warranty)' festival> (voice_name_here) from the list of voices returned by typing festival> (voice.list) works, then there must be a way to get the program to interpret its own scheme expressions via the command line too, right?