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From: peter@ficc.ferranti.com (Peter da Silva)
Newsgroups: comp.lang.misc
Subject: Re: Re^2: Some things that pointer-less languages can't do efficiently
Message-ID: <+CI6:YD@xds13.ferranti.com>
Date: 18 Oct 90 20:35:43 GMT
References: <26739:Oct1023:44:2690@kramden.acf.nyu.edu> <65450@lanl.gov> <10397:Oct1212:55:1090@kramden.acf.nyu.edu> <3975@goanna.cs.rmit.oz.au> <415@data.UUCP>
Reply-To: peter@ficc.ferranti.com (Peter da Silva)
Organization: Xenix Support, FICC
Lines: 25

In article <415@data.UUCP> kend@data.UUCP (Ken Dickey) writes:
> There are a number of programming languages, Scheme and ML among them,
> which do not have a pointer abstraction.

The *only* abstractions in scheme are a pair of pointers or a value.

> [After programming in Scheme for a few days, no
> one ever "falls off the end of a pointer chain" or "defererences a
> bogus pointer"].

Sure. If you've got data in a list, say:

	("da Silva" "Peter" "ferranti.com" "peter")

And you accidentally return (cdr list) instead of list, you have all the
problems as you do in C when you return a pointer to the middle of the
array. Oh, sure, the *symptoms* are different, but when you have an
object (a C pointer, or a dotted pair) that can point to any arbitrary
place in any non-atomic language object (a string, or a list) you have the
exact same problem.

This is not to say that scheme doesn't make the consequences of falling
off a list or taking the cdr of a bogus pair less dire, but claiming
that languages like scheme "don't have a pointer abstraction" is going
a bit far.
-- 
Peter da Silva.   `-_-'
+1 713 274 5180.   'U`
peter@ferranti.com