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

Good bye
by Glavitsch Eggler Ulrike Alexandra 23 Jul '10

23 Jul '10

Dear all, As some of you may know I left ETH by the end of May. I have enjoyed five years of intense systems programming with A2 and want to thank you for all your ideas, suggestions, bug reports, etc. to improve A2. I hope that A2 will make it to a usable, highly competitive operating system. I am a member of the Media Technology Group (www.empamedia.ethz.ch) at Empa in Dübendorf since July 1, 2010 (www.empa.ch) And I hope that one day I can program one of the group's future applications in Oberon. Let's keep in touch and best regards Ulla Glavitsch PS: My ETH email will be valid until the end of the year. But you better reach me under ulrike.glavitsch(a)empa.ch.

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open array usage
by spir 14 Jul '10

14 Jul '10

Hello, Sorry for coming back to the topic, but I still cannot figure out how open arrays are supposed to be used in Oberon, without any form of literal notation. PROCEDURE Sum(reals:ARRAY OF REAL) : REAL ; PROCEDURE Max(reals:ARRAY OF REAL) : REAL ; How can one pass [1,2,3] or [a,b,c] to one of those procedures? TYPE STRING = POINTER TO ARRAY OF CHAR ; PROCEDURE concat(ARRAY OF STRING) : STRING ; PROCEDURE write(ARRAY OF STRING) ; How can one concat or write ["Hello, ", name, ", how do you do?"]? Is there an answer? If not, how to achieve that, or anyhow work around the issue? Side-question: how to define an Oberon equivalent to Pascal's write? Denis ________________________________ vit esse estrany ☣ spir.wikidot.com

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Possible typo in Zonnon EBNF description
by Aubrey.McIntosh＠Alumni.UTexas.Net 13 Jul '10

13 Jul '10

I am looking at section /11. Constants on page 57 of the July 28, 2009 Zonnon language report. The production ScaleFactor includes the term ["+" | "" ] I suspect this should be ["+" | "-" ] -- -- Aubrey McIntosh, Ph.D. 1502 Devon Circle Austin TX 78723-1814 http://home.grandecom.net/~amcintosh/aubrey/Search/

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Oberon
by Josef Sedlacek 12 Jul '10

12 Jul '10

Dear colleges Once more we have a dispute about the quality of Oberon. What a surprise that it is possible to judge about a work of many people during a long time in such direct way by using the word string. Best regards Josef Sedlacek -- Company: Radiar, Dr. J. Sedlacek, CH-7554 Sent Tel: +41 (81) 860 06 60 Fax: +41 (81) 860 06 62

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concrete use of open array -> functional-style
by Chris Glur 11 Jul '10

11 Jul '10

Cc: Newsgroups: --- spir wrote > > Right, I will need such a pattern for higher-order funcs. Not that > > I appreciate the functional paradigm, No ! functional style gives great advantages. > > but some match typical patterns, > > eg for collections (find --> element; filter, map --> collection; > > any, every --> boolean). I particuliarly like the clarity of code > > 'every' enables: > > IF numbers.every(isNaturalNumber) THEN ... > > IF objects.every(isNotNil) THEN ... > > IF inputData.every(isValid) THEN ... This is what we need. Joerg wrote:- > You're right, Oberon does offer e.g. ARRAY OF REAL but > no higher functions like "filter" or "every" that work on it > natively. > > The good news however: these functions can be added if needed. > The higher data type (Element, Collection..) and their > corresponding functions (find, filter, every..) are encapsulated > in a MODULE. Instantiation, input and output of those > higher data structures should be handled in this MODULE as > well. I'm sure someone has already done this. Let's have what's already been constructed! Although I've used ETHoberon every day for decade/s, I've never written any code as substantial as I wrote previously in turbo-pascal. Since we 'must' base our code on the existing S3 framework, and extend it, I'm repeatedly frustrated when instead of say: StoreTo(FileName, ... , I see in every one of the many sources that need to get the filename from <ID>, "*" or "^", the use the tedious routine of: * declare auxiliary varaibles, * intialise var-args, * call * unpack returned values from the assembly code mentality, sources. We discusssed this before, and I suspected that because ETH is a teaching intitution, 'each student must have done the "exercises" to graduate', instead of just calling the low-level routines which were previously written, via "well factored code". I.e. each student must get practice in inventing the wheel? With initial skeptisism, I've recently been following the debate about functional languages eg. :---- extract -------- http://www.onlamp.com/pub/a/onlamp/2007/05/21/ an-introduction-to-haskell---part-1-why-haskell.html If I want to define a function that takes a list of values, and returns only the even values in that list, it would look like this in the interpreter: Prelude> let evens = filter even -- define the function Prelude> evens [1..10] -- filter numbers out of a list [2,4,6,8,10] This example may appear trivial, but it demonstrates a key benefit of working with lambda calculus in a functional programming language -- the ability to create specialized functions by merely gluing together a small number of more generalized, pre-existing functions. Interestingly, this is exactly how shell pipelines work. Writing the function evens in C is much more complex. First, the output list must be allocated, and to do that, the number of output values must be counted. Next, the values must be copied to the new list, one at a time. This simple expression in Haskell becomes this function in C: int *evens(int *in, int count) { int matches = 0; int i, *out, *ptr; for (i = 0; i < count; i++) { if ((in[i] % 2) == 0) { matches++; } } out = malloc(sizeof(int) * matches); ptr = out; for (i = 0; i < count; i++) { if ((in[i] % 2) == 0) { *ptr = in[i]; ptr++; } } return out; } This function defines the combined behavior of the Haskell definition of evens. That is, this block of code is equivalent to the expression 'filter even' in Haskell. If there were a C library function that handled the behavior of filter, this code would be simpler. However, this is kind of solution is sadly idiomatic in C-like languages. -------------- end of extract ------------- What broke my initial skeptisism against functional/concatinative languages' claims was that I started writing an ETHoberon utility to transform eg:- > Lambda calculus is spurious-spaces nothing more than a precise set of rules that ==too-long-line describe how > to evaluate functions. to > Lambda calculus is spurious-spaces nothing more than a precise > set of rules that ==too-long-line describe how to evaluate > functions. and abandoned it through frustration of having to grovel at low level. Since I use mostly linux-ETHoberon these days, I checked for a linux solution; ie. that uses existing functions piped together. The whole utility is a few characters which is tested incrementally while being designed. I'm GUESSING [because I don't WANT to remember] that it does something like: write the text lines through a filter that: removes multiple spaces, and cuts the lines to (len < N) at word-boundries, and if the first line started with "[>]{' '}" then let all new-lines start similarly. ------- How many of you have tried ETHoberon's Scheme.Tool? Quite remarkable. I haven't tried LayLa yet! I've got no doubt that very powerful higher levels of abstraction can be conveniently built with ETHoberon. Perhaps some tools already exist in the above described direction? == Chris Glur. PS. a further example, that I use every day, that reminds me of the power of 'composing functions' [stringing filters in series] is: FindTelephoneNumber(someone), where I know that my telephone-directory is in the <root-dir> of <one of my partitions>. So I just need to 'compose' the 3 simple concepts. 1=show me the list of mounted partitions and use my selected one, because I don't want to remember, and I'll recognize, when I see it. == df 2=and list the file-name/s "*ele*" == ls "*ele*" 3=and list the line/s which contain "<someone>" == | grep someone NB. this case is done interactively, because I want to recognise the partition's name and be able to humanly select the recognised <telephoneDirectory> filename. --------- These people who write *nix scripts, have no difficulty in writing one-liners to eg. :- list all the File-IDs with the lines containing <string>, which were written in June or July, between 1994 and 2007 - inclusive; and reverse-order the lines by non-white-char count. PSS. I've just remembered how astounding ETHo's Vinci tool is; which is built on scheme, which is built on oberon. Unfortunately, automating the creation of drawings is a very specialised application, not needed by many. But hi-level functions to manipulate text in files are needed every day. Such facilities, which exist for *nix, give massive productivety increases. I'm confident that we too could have them, as oberon-users.

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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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