Since the topic of using BASIC as part of the test suite for Parrot has been brought up before I'll mention a recent change I made here which might make this easier.
If the BASIC interpreter is invoked now, and a file named "autorun.bas" exists in the same directory, it will be run by the interpreter auto-magically on startup. At the moment I'm using this to run the BASIC regression test while I'm modifying the interpreter so I can just say (in vim): !basic.pl Have it assemble up BASIC, run the test (which had been renamed to autorun.bas) and exit back to vim. Earlier this evening I was using it to run a BASIC CGI script (just for kicks). Making the last instruction "QUIT" will exit the interpreter when autorun.bas is finished running; making the last instruction "NEW" will clear memory and leave you in interactive mode. Otherwise you're dropped into interactive mode when the program's done running.