June 2010 - Oberon - mailman3.inf.ethz.ch

0X enigma
by spir 03 Jul '10

03 Jul '10

Hello, My in-progress custom Text type had a strange behaviour in case a text is initialised with 0X (I rely on the fact that a character is automatically converted to an ARRAY OF CHAR, which is the type of the formal parameter of the method Text.init). Any other case works fine. As a trial to elucidate the issue, I wrote the following test: MODULE ___trial___; IMPORT Out; VAR chars : ARRAY 4 OF CHAR; PROCEDURE show(chars:ARRAY OF CHAR); BEGIN Out.LongInt(LEN(chars),0) ; Out.String(' : ') ; Out.String('|') ; Out.String(chars) ; Out.String('|') ; Out.Ln ; END show; BEGIN chars := 'abc' ; show(chars) ; show('abc') ; show('a') ; show(61X) ; show('') ; show(0X) ; END ___trial___. === output === 4 : |abc| 4 : |abc| 2 : |a| 2 : |a| 1 : || 2 : || I thought and read that 0X is equivalent to ''. It is equivalent for output, since 0X produces none per definition; but its internal representation is not the same. This indeed fools my code (or rather my initial assumption): the init method records an actual content size of 1. Actually, this behaviour may be better, allowing the user to define a String really containing a single char (or byte) that actually holds 0X. But I would like to elucidate the enigma anyway. Denis ________________________________ vit esse estrany ☣ spir.wikidot.com

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concrete use of open array
by spir 02 Jul '10

02 Jul '10

Hello, I start to get a feeling of Oberon's style (I guess). Seems it requires programmers to build their toolkit, even for very basic, everyday, all-purpose, little tiny tasks (even more than eg Lua, which reputation reads "DIY"). Comments? Some details still escape my understanding, esp. around open arrays -- again. -1- form of actual parameter Since one cannot have a VAR of open array type, what is the actual form of an open array parameter, in the call expression? I tried the "[...]" format used in some Pascal dialects to express open array constants, but it is refused. Side-question: is there a literal notation for arrays? for records? (eg like pascal consts, or var initialisation) -2- COPY vs assignment The following is accepted by obc but refused by oo2c [EDIT: the opposite, in fact!]. Note that t1 & t2 share a unique & named type. In the latter case, I need to use COPY instead of :=. MODULE trial; TYPE ToChars = POINTER TO ARRAY OF CHAR; VAR i : INTEGER; t1,t2 : ToChars; BEGIN NEW(t1,3) ; NEW(t2,3); FOR i := 0 TO 2 DO t1[i] := CHR(97+i) END; t2[3] := 0X; t2 := t1; (* COPY(t1^,t2^); *) (* output routine *) END trial. But COPY removes the last element by replacing it with 0X, whatever lies there in the source array. My use case is a flexible array, of which a char sequence is only a particuliar case, which holds a 'size field' (so that getting the size does not require sequence traversal). Also, arrays of chars are commonly used as byte sequences. (Even more on Oberon since there is no BYTE?) Is there a way to make assignement work between all kinfs of open arrays? -2- size & copy Assignment/copy between arrays of different sizes does not seems to be possible, or at least I could not have it work (neither is the case where dest >source, nore the opposite). About COPY, the report says the dest if truncated if necessary, but even this does not work with the compilers I use. Is there a way to express: a2 := a1[i..j]; a2[i..j] := a1; ? -4- allocation Say I'm writing a func returning the indices of occurrences of a given element in a collection. I guess the only possible return type is a pointer to an open array. Correct? But how to allocate it (NEW(indices,size)), since its size is also a result of the process (collection traversal)? The only solution I found is two traverse twice ;-): once to count and then allocate, once to feed the array. off-topic: * is it possible to rename imported procs (eg "Write := Out.String" :-)? * alternatives to "(**)" such as "{}" or "//"? My editor deals badly with "(**)", transforming comments into visual pollution; and not permitting comment-in/out toggling. Denis ________________________________ vit esse estrany ☣ spir.wikidot.com

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memory freeing
by spir 30 Jun '10

30 Jun '10

Hello, When I resize the array actually holding a sequence's elements, the previous array is lost. In C or Pascal, I should free it, since it is dynamically allocated (in heap, certainly); but there is no such statement (free, release) in Oberon AFAIK. The report speak about GC, but this is in the informative part presenting some aspects of Oberon-the-system as an example environment for Oberon-the-language. oo2c, the compiler I presently, indeed can be built to use a GC (and I did it). So, I should be safe. But this does not solve the issue in the general case. What should I do? Thank you, Denis ________________________________ vit esse estrany ☣ spir.wikidot.com

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languages and programming libraries and
by peasthope＠shaw.ca 25 Jun '10

25 Jun '10

From: denis.spir at gmail.com (spir) Date: Tue Jun 22 12:28:03 2010 > If there is no builtin way to handle strings practically, ... From: Aubrey.McIntosh at Alumni.UTexas.Net Date: Thu Jun 24 21:55:55 2010 > probable that the library exists that will allow you to program > a solution to whatever problem you are trying to solve. >From chris at cfbsoftware.com Wed Jun 23 02:37:13 2010 > The great advantage of local dynamic arrays is that they can be safely > allocated on the stack. Thus no garbage collector or special treatment ... Years ago, an instructor in a CpSc course here stressed the idea of a formal language designed for a purpose rather than one language for diverse purposes. According to that approach, I'd think of Denis using an interpreter for J or K for his project. That would provide the array manipulation and interactivity he described. Of course this assumes implementation of the language interpreter; not a small matter. Regards, ... Peter E. -- Carnot is down, waiting for installation of NetBSD. Personal site works; http://members.shaw.ca/peasthope/ .

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string manipulation
by spir 23 Jun '10

23 Jun '10

Hello, I'm an amateur programmer, completely new to Oberon. Is this a proper place to find help in learning the *language*; and to talk about it? If yes, I have a first question: strings are defined as sequences of characters. But this only seems to define pieces of text in literal notation; there is I guess no corresponding type. If I get it correctly, then we are supposed to store and manipulate strings in ARRAYs OF CHAR, which will automatically be 0-terminated: "If an expression e of type Te is assigned to a variable v of type Tv, the following happens: ... if Tv is ARRAY n OF CHAR and e is a string of length m <n, v[i] becomes ei for i = 0..m -1 and v[m] becomes 0X. " But this type is a bit unhandy, esp in the fact it cannot be RETURNed. How are we supposed to deal with strings concretely? For instance, how can I write a procedure text intended to allow outputing a Position: MODULE aTrial; IMPORT Out; TYPE Position = RECORD x : INTEGER; y : INTEGER; END; PROCEDURE (VAR pos:Position) text() : ???; VAR t : ARRAY OF CHAR; BEGIN RETURN ???; (* "x:pos.x,y:pos.y" *) END; VAR pos : Position; BEGIN pos.x := 1; pos.y := 2; (* write pos.text to stdout *); END aTrial. If there is no builtin way to handle strings practically, how can one build a custom tool (a type) for this? I'm aware I could use POINTER TO ARRAY OF CHAR to pass strings around (*), but then I need to explicitely (de)reference all strings. Another point about strings is the common need to output variable values (for examples, prototyping, testing...). Maybe it's only me beeing blind, but I cannot even find builtin tools to output atomic values... not to evoke arrays or records. Denis (*) Like in the example Trees module at §11 of the Oberon-2 language report. ________________________________ vit esse estrany ☣ spir.wikidot.com

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ARRAY OF CHAR mystery
by spir 22 Jun '10

22 Jun '10

Hello, In an attempt to build a string abstraction as evoked in the previous theread, I'm blocked with the following issue: I find myself unable to assign an ARRAY OF CHAR value to an ARRAY OF CHAR variable. Below pchars is of type POINTER TO ARRAY OF CHAR. The statement pchars^ := chars; is refused. Below results of compilation with oo2c and obc: oo2c --make "trial.Mod" (in directory: /home/spir/prog/oberon) Compilation failed. /home/spir/prog/oberon/trial.Mod:16:15: Expression not compatible with variable type `ARRAY' obc "trial.m" (in directory: /home/spir/prog/oberon) Compilation failed. "trial.m", line 16: type ARRAY OF CHAR is needed on the RHS of this assignment > pchars^ := chars; > ^^^^^ > This expression has type ARRAY OF CHAR obc's message is very nice ;-) A side issue is that I cannot find another way to return an array or a record other than via a pointer. Meaning eg a Text type would actually need to be a type of pointers to actual string data. But pointers break clear and secure value semantics, in that after t2 := t1; any change to either text affects both. One is thus forced to explicitely dereference all string variables: t2^ := t1^; I also find myself forced to build the string data self as a record to be able to affect it various needed methods. So, I end up as of now with the following: TYPE Chars = ARRAY OF CHAR; PChars = POINTER TO Chars; DText = RECORD (* actual text data *) pchars : PChars; count : LONGINT; isEmpty : BOOLEAN; END; Text = POINTER TO DText; But I'm blocked, as explained above, in assigning pchars^ at creation of a Text. denis ________________________________ vit esse estrany ☣ spir.wikidot.com

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Noob Q: Can I discuss Aos here?
by Duke Normandin 11 Jun '10

11 Jun '10

Hello list... Would it be appropriate, or should I restrict my questions to the "language" only? -- duke

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Noob Q: Programming in Oberon while in Aos
by Duke Normandin 09 Jun '10

09 Jun '10

Back again... I've never been exposed to Aos - "the system", or Oberon - "the language". I want to test-drive Oberon (the language) while in Aos. How would I go about doing that? TIA.. -- duke

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Noob Q: Meta key for Aos on MacOS X Leopard
by Duke Normandin 09 Jun '10

09 Jun '10

Hey list... Can't seem to get a "Meta" to work while in Aos, which is running on top of X-Windows on my MacOS X box. Any clues? -- duke

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