and which of those are likely to be used professionally (if lisp could be used for such)?<p>I don't have any experience with lisp or with any of its variants but I've seen a lot of codes written in it.
You could ask why there are so many text editors out there? Basically, people have found things that they wanted to be different so they came up with custom versions to scratch their itch.<p>Whilst there are lots of variants, the three main ones to consider are:<p>Scheme, standard is R7RS - more academic and research oriented. SICP book is a fantastic resource.<p>CommonLisp, standard is ANSI X3.226 - mostly used in commercial applications<p>Clojure, useful for interoperability with Java Virtual Machine.<p>Lisp is the "secret weapon" of many businesses, e.g. Paul Graham wrote ViaWeb in CommonLisp. Brendan Eich was really planned to implement a Scheme variant, but had to wrap it into a C-like syntax and call it JavaScript for marketing reasons. Emacs (the editor) uses eLisp.<p>If you are thinking of using Lisp professionally, then CommonLisp is probably your best bet. Once you know one Lisp, you can easily transfer the bulk of your knowledge to other variants.
Because they're easy to make and easy to experiment with, and it's fascinating.<p>Lisp is used professionally in lots of places, just not the most mainstream ones. Common Lisp, Clojure, Scheme, and others. And Hacker News is written in Arc, so we use Lisp professionally here.