Path: utzoo!attcan!uunet!lll-winken!ames!mailrus!csd4.milw.wisc.edu!uxc!tank!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.lang.misc
Subject: Re: What is B&D? (Re: Bondage and Discipline Languages)
Message-ID: <15458@mimsy.UUCP>
Date: 13 Jan 89 13:47:01 GMT
References: <8540@megaron.arizona.edu> <2630@ficc.uu.net> <13293@cup.portal.com> <5818@medusa.cs.purdue.edu>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 55

>David Gudeman writes:
>>You don't lable a language ``B&D'' just because you can't do something
>>in that language, you call it that because (1) there is something you
>>can't do, (2) the designers of the language predicted people would
>>want to do it, and (3) the designers deliberately made it impossible
>>because they thought it was a bad thing to do.

In article <5818@medusa.cs.purdue.edu> rjh@cs.purdue.EDU (Bob Hathaway) writes:
>This sounds like you don't know programming as well as compiler writers,
>language designers, programming language hobbyists, ...  I, and several
>others I have talked to can do anything we can do in C in Pascal, Modula,
>Ada, etc.

The point is not whether the ultimate goal can be accomplished (the
answer is almost always `it can'), but rather whether the means by
which you wish to accomplish it has been ruled out in advance.

My favourite example (as of the last time I gave an example, anyway :-) )
of this is the classical list-building loop:

	var head, tail, l : list;

	head <- nil; tail <- nil
	for ever do
		l <- get_input
		exit when l = nil
		(if head = nil then head else tail.next) <- l
		tail <- l
	rof
	return head

This algorithm works fine in Pascal, C, etc.  But the way I prefer to
write it in C is this:

	struct list **p, *l, *head = NULL;

	p = &head;
	while ((l = get_input()) != NULL) {
		(*p)->next = l;
		p = &l->next;
	}
	return head;

You *cannot* write this algorithm in (standard) Pascal, because it
will not let you compute the address of `head' or that of `l->next'.
There are reasons for that, but they amount to what David said:

	>>and (3) the designers deliberately made it impossible
	>>because they thought it was a bad thing to do.

(and maybe it *is* a bad thing, but that is irrelevant to the label
`B&D').
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris