Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!brutus.cs.uiuc.edu!psuvax1!psuvm!trl3 From: TRL3@psuvm.psu.edu (Tim Larson) Newsgroups: comp.lang.modula2 Subject: Re: BY expression Message-ID: <90033.103548TRL3@PSUVM.BITNET> Date: 2 Feb 90 15:35:48 GMT References: Organization: Penn State University Lines: 37 Questions of this type can often be answered by looking at the motivation behind the designer(s) of a programming language. I read an article once (which I tried to find, but could not), I think by Wirth or another person closely associated with the Lilith project, about why Modula-2 was designed. It seems to me that Modula-2 was designed for a specific project---as a high- level equivalent or substitute for assembler. The Lilith computer and the family of system languages that include Modula-2 were essentially designed together. For example, the Lilith has specific machine code instructions that aid in executing programs written in Modula-2 for the Lilith. Thus, although Wirth was motivated to write the best possible systems language for this project, that does not mean it is the best possible language for all systems. (Of course, "best possible" does not mean perfect or even uniquely best.) As it happened, however, Modula-2 got a lot of attention and was found to be relatively portable and (unlike Ada and C) simple. Now, Modula-2 has become more than just Wirth's language and is proceeding to an inter- national standard (just as Pascal did before it). Wirth has apparently moved on to a newer member of the Modula family called Oberon which simplifies the language even more, but at the same time adds some object-oriented features. Good Lord...I didn't mean to write this much, but I guess that the answer is that in many cases, Wirth designed features of the language to be closely coupled with a specific machine since it was the principle systems language of that machine. Consequently, simple things like BY have what may seem to us like odd semantic restrictions, though they would not be so odd in what is essentially an assembly language environment. (Stepping off my soapbox ...) -Tim Larson trl3@psuvm.bitnet P.S. If anyone can remember the article I mentioned from my rather limp description of it I am now dying to know. Naturally, this rambling article came from memory and I do not discount the possibility that a few cosmic rays may have scrambled some of my neurons over the years, so any inaccuracies are entirely due to me.