Xref: utzoo comp.lang.misc:1990 comp.lang.lisp:1157
Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!apple!bionet!agate!labrea!decwrl!sun!pitstop!sundc!seismo!uunet!mcvax!ukc!eagle.ukc.ac.uk!icdoc!qmc-cs!harlqn!jcgs
From: jcgs@harlqn.UUCP (John Sturdy)
Newsgroups: comp.lang.misc,comp.lang.lisp
Subject: Re: reflexivity
Keywords: reflexivity,meta-circularity
Message-ID: <1279@harlqn.UUCP>
Date: 12 Oct 88 10:55:16 GMT
References: <612@crin.crin.fr> <826@etive.ed.ac.uk>
Reply-To: jcgs@uk.co.harlqn (John Sturdy)
Organization: Harlequin (Cambridge, UK) Ltd.
Lines: 21

In article <826@etive.ed.ac.uk> sean@lfcs.ed.ac.uk (Sean Matthews (AI)) writes:
>In article <612@crin.crin.fr> napoli@crin.crin.fr (Amedeo NAPOLI) writes:
>>Does anybody have clear definition of the following terms:
>>- meta-circularity, reflexivity, self-reflexivity
>
>reflection is where a programming language has access to its own interpreter,
>and can modify it.
Or a finer distinction:
Reflection is where a program can modify its own text, and modify its
"internal" state, as ordinary data objects
Reification is where it can access (read) its text and state
Tower reflection and reification are where it can access its interpreter's
text and state (and its interpreter's interpreter's text and....)

To take examples from "ordinary" programming languages:
setjmp in the C/un*x library is a reifier, and longjmp is the corresponding
reflector. They move information between the "interpreter state" (CPU
stack and PC registers in this case) and the program's data space.
The "varargs" mechanism is just about a reflective device, too.

__John (jcgs@uk.co.harlqn)