Almost nothing. It makes a great deal of sense to make something fun and throw it away. Pick some frameworks to make it easier (parser, and perhaps a compiler o

Almost nothing. It makes a great deal of sense to make something fun and throw it away. Pick some frameworks to make it easier (parser, and perhaps a compiler or interpreter toolkit) and make a throwaway. There's no such thing as 'language clutter'. No-one is harmed by you making a pet language for your own edification, and you will almost certainly not build anything that's more useful than an existing language on your first try. Or even first N tries. It's very educational, it does no-one any harm, and it's really fun when something works. Just don't take yourself too seriously.