🚀 go-pugleaf

in article <8901180542.AA20739@yorkville.csri.toronto.edu>, sam@csri.toronto.edu (Samuel Weber) says:
> In article <eeuqR#3lcVcX=eric@snark.uu.net> eric@snark.uu.net
>>In article <1226@indetech.uucp>, david@emerald.UUCP (David Kuder) writes:
>>> Speaking of *obvious* examples, what isn't a B&D language?
>>C. C++. Lisp. Basic. Fortran. Any assembler. 
> What!!!  I am willing to admit that Lisp might not be B&D, but C and
> C++ are unquestionably one of the worst bondage and disipline languages
> around!  Both of these languages force one to adhere to an artificial
> program/data distinction, as if there was some carved-in-stone
> declaration of which bytes happened to be code, and which data.  If
> I want to write self-modifying code, and the language prevents me
> because the designer thought that self-modifying code was a 'bad
> thing',

Note that self-modifying code will break on most processors with
seperate C-cache and D-cache. The D-cache is usually write-through,
but not the C-cache. Writing code through the D-cache won't update the
cached code in the C-cache.

Also note that most modern operating systems (e.g. BSD4.[23]) page
code directly from the object file, and share this RAM image between
all instances of the running program. E.g. if you have four Emacs's
running, you only have a single instance of the code segment shared
amongst all four Emacsen. Self-modifying code would mean that the code
segment would no longer be sharable, meaning a MUCH higher
swapping/paging overhead. 

There are good reasons for not having self-modifying code. It is thus
silly to say that a language is "B&D" for not supporting it.

Re: what is NOT B&D: How about "any language in which you can write a
device driver is not B&D." Unfortunately, it's just as easy to write a
device driver in Pascal or Modula II as it is in "C" (although you
have to use unions to do so). 

> especially irritating is that even though many people, such as the
> designers of Lisp, approved of self-modifying code, the designers
> of C and C++ decided to single-handedly legislate it out of existance.

Hardware and OS designers legislated it out for efficiency reasons.
Self-modifying code in Lisp runs in the D-space, and is NOT shared
amongst processes. This has an obvious efficiency hit when you have
ten people all on the same system running that program.

--
Eric Lee Green    ..!{ames,decwrl,mit-eddie,osu-cis}!killer!elg
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