Leave it to XKCD to figure out the last word on this :-) http://www.xkcd.com
On Wed, 2011-07-20 at 10:22 -0400, daly wrote: > On Tue, 2011-07-19 at 22:16 -0700, Sean Corfield wrote: > > On Tue, Jul 19, 2011 at 5:14 PM, Adam Richardson <simples...@gmail.com> > > wrote: > > > the value placed on the last language being > > > homoiconic (without much justification) > > > > Yeah, that was definitely a weak point of his talk. I thought there > > was a lot of interesting stuff in there tho' and it was entertaining > > (which was mostly why I enjoyed it - so many talks, even keynotes, can > > be pretty dull even if the information is good :) > > A justification of homoiconicisty is that programs == data. > > A clever soul named Von Neumann made the observation that machines > were controlled by external commands (i.e. programs) to operate on > things (i.e. data). His insight was to unify the problem and treat > programs as data resulting in the invention of the stored program > computer. > > If you completely separate something like a loader (program) from > its data (the binary program) then there is no way to treat the > program-you-load as the-program-to-run. > > Today we teach students to write "programs to manipulate data" so we > have returned to the pre- Von Neumann mindset. It is considered the > height of bad form to execute data. In fact, some bright spot > added SELinux with the default policy that you could not > execute code from the heap! > > Robert gave an example of self-modifying behavior with the IBM > move instruction where he talked about modifying the length field > dynamically. In fact, the IBM 370 included an EX instruction that > executes another instruction with modifications. Both of these are > easy to do since the program and the data have the same binary > representation. > > In your best language (e.g. C++, Python, Ruby, etc) can you write > a program that modifies itself in the source language (e.g. C++) > while continuing to execute? Would this be considered a bug during > code review? (Fortran used to allow me to write over the FORMAT > output string which allowed me to change the output format based > on the data.) If you do write a self-modifying program, did you > have to write a C++ parser first? In lisp, all you have to do is > walk the program as a list, rplaca the target sublist, and continue. > > Fortunately someone at Sun was able to cross this barrier when they > decided to write the hotspot JVM. Hotspot self-modifies as it runs > to improve performance, similar to the Rubics cube program I > mentioned previously. I wish they had been mindful enough to make > Hotspot a fundamental part of Java itself. We would be able to write > Java programs that self-optimize in ways that Hotspot cannot know > by accessing and rewriting our own byte codes. If someone reifies > the byte codes in lisp syntax it would be easy to write programs > directly on the JVM that look like lisp, compiles to byte codes, > and could be self modified. > > Homoiconicity is Von Neumann's insightful idea that > programs == data > > > > -- > > Sean A Corfield -- (904) 302-SEAN > > An Architect's View -- http://corfield.org/ > > World Singles, LLC. -- http://worldsingles.com/ > > Railo Technologies, Inc. -- http://www.getrailo.com/ > > > > "Perfection is the enemy of the good." > > -- Gustave Flaubert, French realist novelist (1821-1880) > > > > -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
