Xref: utzoo comp.lang.misc:1121 comp.lang.modula2:669
Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!pasteur!agate!ig!uwmcsd1!bbn!rochester!crowl
From: crowl@cs.rochester.edu (Lawrence Crowl)
Newsgroups: comp.lang.misc,comp.lang.modula2
Subject: Re: From Modula to Oberon
Message-ID: <7321@sol.ARPA>
Date: 2 Mar 88 21:57:12 GMT
References: <7161@sol.ARPA> <2787@enea.se>
Reply-To: crowl@cs.rochester.edu (Lawrence Crowl)
Organization: U of Rochester, CS Dept, Rochester, NY
Lines: 25
Keywords: Enumerations, subranges, arrays, FOR, Eiffel

In article <2787@enea.se> sommar@enea.UUCP(Erland Sommarskog) writes:
>The extended type facility is a nice feature, but principally it's just
>another way of expressing prefix classes, well-known from Simula. A somewhat
>different approach is Ada's generic packages with private-type parameters.

Ada's generic packages may introduce a new procedure to handle each parameter
type.  Oberon's extended types guarantee that exactly one procedure is needed.
Ada's generic packages allow only one type to be in the corresponding
structure (e.g. queue), while Oberon's extended types allow many different
types to be in the queue.  Ada's generic packages allow putting a type on a
queue to be done simply as an afterthought, but using Oberon's extended types
requires the more effort to put a type on a queue as an afterthought.

>The idea of having all arrays starting on index zero is really to put the
>burden on the programmer. ... And his argument about saving execution time
>for index computation is truely naive. The result will just be references
>like: "String(char_no + 1)", just making the code more verbose and complex
>for no use.

One compiler technique adjusts the "base" address portion of the index
computation to account for non-zero lower element.  This optimization becomes
harder if non-zero basing is done in user code.
-- 
  Lawrence Crowl		716-275-9499	University of Rochester
		      crowl@cs.rochester.edu	Computer Science Department
...!{allegra,decvax,rutgers}!rochester!crowl	Rochester, New York,  14627