def warn(msg, level=<NUM_LIT:0>, prefix=True):
if will_print(level):<EOL><INDENT>printer(("<STR_LIT>" if prefix else "<STR_LIT>") + msg, "<STR_LIT>")<EOL><DEDENT>
Prints the specified message as a warning; prepends "WARNING" to
    the message, so that can be left off.