[Oberon] string manipulation

Tue Jun 22 17:50:11 MEST 2010

It is not possible to de-reference a pointer returned by a function in
an expression.  So the following code is as close as I can get, with a
pointer assignment, and the pointer then dereferenced.

MODULE aTrial;
IMPORT Strings, Out;

TYPE
       Position = RECORD
               x       : INTEGER;
               y       : INTEGER;
       END;

	String = ARRAY OF CHAR;
	StringPtr = POINTER TO String;

VAR pos : Position;

PROCEDURE (VAR pos:Position) text(): StringPtr ;
	VAR
		string : StringPtr;
BEGIN
	NEW( string, 24);
	(*integer to string conversion here.*)
	COPY ( "(42, 96)", string^);
	RETURN string
END text;

PROCEDURE Do*;
	VAR
		string : StringPtr;
BEGIN
	Out.String("aTrial.Do ");
	NEW( string, 32 );
	string := pos.text();
	Out.String( string^);
	Out.Ln;
	Out.String("Done.");
	Out.Ln
END Do;

BEGIN
   pos.x := 1; pos.y := 2;
END aTrial.Do

On Tue, Jun 22, 2010 at 10:19 AM, Stauber  Sven Philipp
<sven.stauber at inf.ethz.ch> wrote:
> Hi,
>
>
>>>> Right. But the report only seems to use "string" to denote the result of evaluating literal notations like 'abc'. There is no mention of a string type (unlike CHAR). So, I guess there may well be various string representations (and/or types for them) in a given implementation, but they belong to the implementation. Or do I miss a basic point?
>
> No, you're right. For those Oberon implementations (e.g. Native Oberon, A2, ...) I've seen, string representation and manipulation is mainly part of the Oberon "system", not the Oberon language.
>
> The only things the Oberon language provides:
>
> - string literals
> - built-in COPY function
> - Operators: = # < <= > >= also work on 0X-terminated "strings"
>
> More advanced string manipulation features as appending a string to another, for example, are implemented as library (as Strings.Mod in Native Oberon/A2). Even more advanced features as text representation are again part of the implementation.
>
> Best,
> Sven
>
> -----Ursprüngliche Nachricht-----
> Von: oberon-bounces at lists.inf.ethz.ch [mailto:oberon-bounces at lists.inf.ethz.ch] Im Auftrag von spir
> Gesendet: Dienstag, 22. Juni 2010 15:46
> An: oberon
> Betreff: Re: [Oberon] string manipulation
>
> On Tue, 22 Jun 2010 14:24:23 +0200
> "Stauber  Sven Philipp" <sven.stauber at inf.ethz.ch> wrote:
>
>> Hi,
>>
>> > ... learning the *language*; and to talk about it?
>>
>> Be sure you don't miss the A2 Programming Quickstart Guide (http://www.ocp.inf.ethz.ch/wiki/Documentation/Language). Also, there is an Oberon & Active Oberon board on our forum (http://www.ocp.inf.ethz.ch/forum/). On http://www.oberon.ethz.ch/bibliography/publications you'll find some "Programming in Oberon" books. Last but not least, there is a lot of code around...
>
> Thank you, I'll follow the pointers. Actually I knew about the forums, but the one ypu mention does not seem very "active": <<Oberon & Active Oberon Programming Languages 1 Posts 1 Topics>>. Also, mailing list are far more practicle for me.
> The core of my interest, as of now, is the *language* Oberon as defined in the Oberon-2 report. I use either 002c or obc to compile for the moment. What is A2, actually? The first sentence of the quickstart guide reads "This is a brief introduction to the programming language Active Oberon and the operating system A2." Implementations including the system or a simulation of it on top of another cannot fit my needs. I may switch to ActiveOberon, again only the language, in a far future, if ever I need to address parallel processing issues, but this is completely outside my field of interests today.
> What I'm looking for is a convenient static and compiled language for a project of mine (actually, a language, too ;-) and to build various tools, mainly for the said project. Oberon-2 seems to be close to perfect.
>
>> > If yes, I have a first question: strings are defined as sequences of characters...
>>
>> Actually, there are several ways how strings are represented. The simplest one is ARRAY OF CHAR for ASCII strings or UTF-8 encoded strings. In A2, the text system represents characters as LONGINT (Unicode) and strings therefore as ARRAY OF LONGINT.
>
> Right. But the report only seems to use "string" to denote the result of evaluating literal notations like 'abc'. There is no mention of a string type (unlike CHAR). So, I guess there may well be various string representations (and/or types for them) in a given implementation, but they belong to the implementation. Or do I miss a basic point?
> If not, the point is then: how are Oberon programmers supposed to deal with strings. ARRAY OF CHAR is an obvious answer but does not hold in practice, since it cannot be the type of a VAR or of a return value. On the other hand, bounded ARRAYs size OF CHAR are not proper types for strings, since very few string variables and return values have a predefined size (indeed, they are the result of input or computation).
> In flexible languages, and in most Pascal variants, there is a type corresponding to the notion of a-piece-of-text and to literals denoting instances of it. My aim is to find the corresponding feature in Oberon-2, or a way to construct such a handy representation myself.
> In the meanwhile, I'll have a look at the source of A2's String type if it's written in Oberon itself & I can find it.
>
>> > ... which will automatically be 0-terminated
>>
>> No, not automatically. It is implementation specific whether some "string" manipulation functions always result in a new "string" (0X-terminated character sequence) or not.
>
> The report explicitely explains that assigning a string (literal) to a var of type ARRAY OF CHAR (which apparently is the only type a var can have to be assigned a string) automagically adds 0X after the string's characters. (The relevant lines of the report are quoted in my original post).
> This is what I meant above.
>
>> [...]
>
>
>
>
> ________________________________
>
> vit esse estrany ☣
>
> spir.wikidot.com
> --
> Oberon at lists.inf.ethz.ch mailing list for ETH Oberon and related systems
> https://lists.inf.ethz.ch/mailman/listinfo/oberon
>
> --
> Oberon at lists.inf.ethz.ch mailing list for ETH Oberon and related systems
> https://lists.inf.ethz.ch/mailman/listinfo/oberon
>
>

-- 
-- 
Aubrey McIntosh, Ph.D.
1502 Devon Circle
Austin TX 78723-1814
http://home.grandecom.net/~amcintosh/aubrey/Search/