They apparently loosened the restrictions on developer tools. For example, I used to have a Scheme interpreter on my iPhone. The problem is that you can't set the executable bit on a memory page, so you can't compile a form to native code and then execute it. You can still have an interpreter, or a byte-code compiler plus a byte-code interpreter, but you lose lisp's ability to compile and run native code. As others have said in this thread, there are workarounds for that, since most lisp applications don't need it, but there's no real reason, other than politics, and a misguided security policy, to forbid it.