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From: chris@umcp-cs.UUCP (Chris Torek)
Newsgroups: net.lang
Subject: Re: Portable Languages
Message-ID: <3909@umcp-cs.UUCP>
Date: Fri, 17-Oct-86 01:16:06 EDT
Article-I.D.: umcp-cs.3909
Posted: Fri Oct 17 01:16:06 1986
Date-Received: Fri, 17-Oct-86 22:22:56 EDT
References: <111@titan.UUCP> <139200039@uiucdcsb> <483@jc3b21.UUCP> <1455@jade.BERKELEY.EDU>
Organization: Computer Sci. Dept, U of Maryland, College Park, MD
Lines: 46
Summary: There is no portability without context

>In article <483@jc3b21.UUCP> fgd3@jc3b21.UUCP writes:
>>Your examples support my point: a _portable_ language is one which
>>runs identically on all implementations.  A language which permits
>>the code generated by its statements to be implementation-dependent
>>is not portable.

You are taking an extreme position; I will be equally extremist.

In article <1455@jade.BERKELEY.EDU> mwm@eris.berkeley.edu (Mike Meyer) replies:
...
>I've got bad news for you. By that definition, the ONLY portable
>languages are ones that are trivially portable, with only one
>implementation.

Indeed.  Convert the following C code to your favourite `portable'
language:

	main()
	{

		printf("\033[H\033[J");
		exit(0);
	}

Now tell me, what does it do on all implementations?  But I have
not defined `implementation' properly: an `implementation' is a
complete system INCLUDING a display device.  *Now* what does it
do? It clears my H19 screen, but it does not clear the screen of
the AJ510 in the machine room.  Ergo, this is not a portable program.

This is a ridiculous stand.  Yet I claim it is little, if any, more
ridiculous than that expressed in article <483@jc3b21.UUCP>.  Every
program must run in a context.  The context can trivially alter the
results of a program.  The essence of portability is the ability to
prevent such alteration within many contexts.

(For precisionists, the program above is indeed unportable in one
sense.  If its purpose is to clear the screen, it is portable only
between environments that use ANSI X3.64 compatible displays.  If,
however, its purpose is to print the string ESC [ H ESC [ J, the
program is portable between all ASCII environments.  Its operation
on an EBCDIC machine is less well defined.)
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 1516)
UUCP:	seismo!umcp-cs!chris
CSNet:	chris@umcp-cs		ARPA:	chris@mimsy.umd.edu