5 ms·

It isn't a LISP :P

• michaf 8y ago
  There is, however, http://www.aosabook.org/en/pypy.html http://www.aosabook.org/en/pypy.html , which is indeed self-hosting.
• coldtea 8y ago
  Doesn't need to be a Lisp. All kinds of interpreters can interpret themselves if they're written in the same language -- similar to bootstraping a compiler.
• chrisseaton 8y ago
  You don't need a language to be a LISP in order for them to be able to interpret themselves. There are several Java interpreters which can interpret themselves, for example.
  • kazinator 8y ago
    You just need it to be a Lisp in order to do it in such a way that you get confused whether you're in the interpreted language or the host one.
    • yorwba 8y ago
      Byterun confuses host and interpreter in plenty of places. It uses the host Python for attribute resolution (all code in getters and setters runs on the host), exception handling (which combines with the previous point to make some NameErrors impossible to catch) and even function calls (but all functions are wrapped so that their _call__ switches back to byterun as the interpreter). Because of that confusion, byterun isn't very useful if you want to be really independent from the host interpreter; it's just too easy to escape from the VM. As a learning exercise however, it is helpful for understanding Python's innards at a level higher than C.
      • kazinator 8y ago
        I mean actually getting confused.
  • CodeArtisan 8y ago
    Do they interpret java, the programming language, or java bytecode? Not the same thing. lisp being homoiconic, it's much easier to implement a metaciruclar evaluator. https://en.wikipedia.org/wiki/Homoiconicity https://en.wikipedia.org/wiki/Homoiconicity
    • chrisseaton 8y ago
      If I gave you a function that accepted Java source code as text and interpreted it, how would you detect that I was first converting it to Java bytecode and then interpreting that bytecode? You couldn't, so it's an irrelevant internal detail. The function interprets Java source code.
      • lispm 8y ago
        > If I gave you a function that accepted Java source code as text and interpreted it, how would you detect that I was first converting it to Java bytecode and then interpreting that bytecode? > You couldn't, so it's an irrelevant internal detail. The function interprets Java source code. In a Lisp interpreter the actual source code is Lisp data, not text. One can give the function access to its source code, allow it to inspect it or even to change it - while the interpreter is executing this source code. In a Lisp interpreter, the code can even modify the source code (we are not talking about the byte-code or machine code) while it is running. CL-USER 20 > (let ((code (copy-tree '(+ 1 2 bar)))) `(defun foo (bar) (print ,code) (unless (eq (first ',code) '-) (setf (first ',code) '-) (foo bar)) (values))) (DEFUN FOO (BAR) (PRINT (+ 1 2 BAR)) (UNLESS (EQ (FIRST (QUOTE (+ 1 2 BAR))) (QUOTE -)) (SETF (FIRST (QUOTE (+ 1 2 BAR))) (QUOTE -)) (FOO BAR)) (VALUES)) CL-USER 21 > (eval *) FOO CL-USER 22 > (foo 41) 44 -42 As you can see the function modified itself so that the operator + was replaced with a - and then called itself again with the same argument. If we now look at the function, we can see that it was indeed changing itself: CL-USER 23 > (pprint (function-lambda-expression #'foo)) (LAMBDA (BAR) (DECLARE (SYSTEM::SOURCE-LEVEL #<EQ Hash Table{0} 41B04012D3>)) (DECLARE (LAMBDA-NAME FOO)) (PRINT (- 1 2 BAR)) (UNLESS (EQ (FIRST '(- 1 2 BAR)) '-) (SETF (FIRST '(- 1 2 BAR)) '-) (FOO BAR)) (VALUES)) The PRINTED expression value is now computed with the - operator. The interpreted execution itself allows also different things then the compiled execution. For example if we have a break point, we can see the actual source code currently executed and we can change it while in the break point and then resume execution. Since the interpreter runs the source code, we can also can modify the interpreter to do something else with the source code, while it is executing it - like recording it or tracing it or stepping it.
  • vram22 8y ago
    Not sure, but I think I read recently (maybe in the Rebol docs) that it is also a homoiconic language. And I think I also read that Rebol programs can interpret chunks of Rebol code passed to them.
    • vram22 8y ago
      I checked: https://en.wikipedia.org/wiki/Homoiconicity#In_Rebol https://en.wikipedia.org/wiki/Homoiconicity#In_Rebol
• niroze 8y ago
  It was a geek joke, I'm not serious. I've written plenty of both languages, even in .gov. Why so serious?!