[Oberon] Re (n): syntax in BB, CP, GPCP and V4 ...

[Hans Klaver]

Jörg wrote:

> Indentation is indeed a totally personal thing.

It is interesting to catalogue the different indentation styles used by some well known (and less well known) programmers of Oberon and Component Pascal source code. With one of the exercises of the Reiser & Wirth book as material I wrote out various indentation styles. 

Crudely four styles of indentation can be discerned:
- No indentation (Daniel)
- Minimal indentation (Reiser / Mössenböck); the difference between the two is in the indentation of declarations (e.g. VAR) at the procedure level
- Classical indentation (Wirth & Gutknecht); has the most consistent indentation of scope levels.
- Knuth indentation (Knuth / Campbell); also quite consistent, but rather convoluted.


MODULE M;  (* After Exercise 6.4 (p. 85) from Reiser & Wirth, Programming in Oberon *)
IMPORT Out;
VAR i, j: INTEGER;
PROCEDURE A*;
VAR i: INTEGER;
PROCEDURE B(VAR i, j: INTEGER);
VAR k: INTEGER;
BEGIN k := i; i := j; j := k END B;
BEGIN i := 2; B(i, j)
END A;
PROCEDURE C*;
BEGIN A; i := 2*j; 
Out.Int(i, 5); Out.Int(j, 5); Out.Ln
END C;
BEGIN
END M.C

(**************************************)

MODULE M;  (* Daniel, http://www.waltzballs.org/other/prog.html#track *)
IMPORT Out;
VAR i,j:INTEGER;

PROCEDURE A*;
VAR i:INTEGER;

PROCEDURE B(VAR i,j:INTEGER);
VAR k:INTEGER;
BEGIN k:=i;i:=j;j:=kEND B;

BEGIN i:=2;B(i,j)
END A;

PROCEDURE C*;
BEGIN A;i:=2*j; 
Out.Int(i,5);Out.Int(j,5);Out.Ln
END C;

BEGIN
END M.C

(**************************************)

MODULE M;  (* M. Reiser, The Oberon System 
     and M. Reiser & N. Wirth, Programming in Oberon *)
IMPORT Out;
VAR i, j: INTEGER; 

PROCEDURE A*;
VAR i: INTEGER;

    PROCEDURE B(VAR i, j: INTEGER);
    VAR k: INTEGER;
    BEGIN 
        k := i; i := j; j := k 
    END B;

BEGIN 
    i := 2; B(i, j)
END A;

PROCEDURE C*;
BEGIN 
    A; i := 2*j; 
    Out.Int(i, 5); Out.Int(j, 5); Out.Ln
END C;

BEGIN
END M.C

(*************************************)

MODULE M;  (* H. Mössenböck, Object Oriented Programming in Oberon-2 *)
IMPORT Out;
VAR i, j: INTEGER;

PROCEDURE A*;
    VAR i: INTEGER;

    PROCEDURE B(VAR i, j: INTEGER);
        VAR k: INTEGER;
    BEGIN 
        k := i; i := j; j := k 
    END B;

BEGIN 
    i := 2; B(i, j)
END A;

PROCEDURE C*;
BEGIN 
    A; i := 2*j; 
    Out.Int(i, 5); Out.Int(j, 5); Out.Ln
END C;

BEGIN
END M.C

(**************************************)

MODULE M;  (* Wirth & Gutknecht, Project Oberon *)
    IMPORT Out;
    VAR i, j: INTEGER;

    PROCEDURE A*;
        VAR i: INTEGER;

        PROCEDURE B(VAR i, j: INTEGER);
            VAR k: INTEGER;
        BEGIN 
            k := i; i := j; j := k 
        END B;

    BEGIN 
        i := 2; B(i, j)
    END A;

    PROCEDURE C*;
    BEGIN 
        A; i := 2*j; 
        Out.Int(i, 5); Out.Int(j, 5); Out.Ln
    END C;

BEGIN
END M.C

(**************************************)

MODULE M;  (* Knuth. E.g. see: http://brokestream.com/tex.pdf *)
    IMPORT Out;
    VAR i, j: INTEGER;

    PROCEDURE A*;
        VAR i: INTEGER;

        PROCEDURE B(VAR i, j: INTEGER);
            VAR k: INTEGER;
            BEGIN k := i; i := j; j := k 
            END B;

        BEGIN i := 2; B(i, j)
        END A;

    PROCEDURE C*;
        BEGIN A; i := 2*j; 
        Out.Int(i, 5); Out.Int(j, 5); Out.Ln
        END C;

    BEGIN
    END M.C

(**************************************)

MODULE M;  (* R. Campbell, Subsystem Lib for BlackBox Component Framework, 
   see the Component Pascal Collection, http://www.zinnamturm.eu/ *)
IMPORT Out;
VAR 
    i, j : INTEGER;

PROCEDURE A*;
    VAR 
        i  : INTEGER;

    PROCEDURE B(VAR i, j : INTEGER);
        VAR 
            k  : INTEGER;
        BEGIN 
            k := i;  i := j;  j := k 
        END B;

    BEGIN 
        i := 2; 
        B(i, j)
    END A;

PROCEDURE C*;
    BEGIN 
        A; 
        i := 2*j; 
        Out.Int(i, 5);  Out.Int(j, 5);  Out.Ln
    END C;

BEGIN
END M.C


Anyone can choose his or her favourite indentation style.

I personally don't like the two extremes (Daniel and Knuth / Campbell). Imho they don't follow Einstein's criterium "Make it as simple as ...": Daniel's is too simplistic and Knuth's / Campbell's are too convoluted.

The classic Wirth / Gutknecht style is the only style that is completely consistent: every scope has its own indentation.
BlackBox uses this style as standard. See: https://hansklav.home.xs4all.nl/ProgrammingConventionsBB.pdf

Some might find the Reiser / Mössenböck styles more aesthetically pleasing because of their simplicity. Although these styles are not as consistent as the Wirth / Gutknecht style, in practice this doesn't matter much because there is only one module scope per compilation unit, and nested procedures are rarely used in Oberon programs.

The latter styles are used in two excellent books: The Oberon System by Martin Reiser and Object-Oriented Programming in Oberon-2 by Hanspeter Mössenböck. These books are the two best typeset Oberon books there are (imho). Unfortunately both have long been out of print. A scanned copy of The Oberon System can be found on the internet here: http://oberoncore.ru/library/reiser_the_oberon_system_user_guide_and_programmers_manual <http://oberoncore.ru/library/reiser_the_oberon_system_user_guide_and_programmers_manual> , and there's a pdf-version of OOP in Oberon-2 here: http://ssw.jku.at/Research/Books/Oberon2.pdf <http://ssw.jku.at/Research/Books/Oberon2.pdf> . In this pdf the source code indentation is not rendered entirely accurately, so also have look at a scanned version of this book: https://books.google.nl/books?id=BseoCAAAQBAJ&printsec=frontcover&dq=object+oriented+programming+in+oberon-2&hl=nl&sa=X&redir_esc=y#v=onepage&q=object%20oriented%20programming%20in%20oberon-2&f=false <https://books.google.nl/books?id=BseoCAAAQBAJ&printsec=frontcover&dq=object+oriented+programming+in+oberon-2&hl=nl&sa=X&redir_esc=y#v=onepage&q=object oriented programming in oberon-2&f=false>

--
Hans Klaver





-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.inf.ethz.ch/pipermail/oberon/attachments/20170725/3bd85d8d/attachment.html>