[Oberon] On Oberon Commands

[Bob Walkden]

> From: Srinivas Nayak [mailto:sinu.nayak2001 at gmail.com]
> 
> Dear All,
> 
>  From Project Oberon Book,
[...]
>     A special facility is introduced for designating viewers as
>     operands: the star marker. It is placed at the cursor position when
>     the keyboard's mark key (SETUP) is pressed. The procedure
>     Oberon.MarkedViewer identifies the viewer in whose area the star
>     lies. Commands which take it as their parameter are typically
>     followed by an asterisk in the text. Whether the text contained in
> a
>     text viewer, or a graph contained in a graphic viewer, or any other
>     part of the marked viewer is taken as the actual parameter depends
>     on how the command procedure is programmed.
> 
> Huh, here I couldn't understand, what is a marked viewer. Which one is
> the equivalent of "keyboard's mark key" in IBM 102 style keyboard? 

F1 normally.

> How
> a
> graph be input to some command? I am not able to understand this
> paragraph!
> 
 
This is one of the things that makes Oberon so interesting. When you
understand the principles of the system the question turns itself upside
down and you ask "Why shouldn't a graph be input to some command?". As Wirth
says in your quote, 'whether the text [...] is taken as the actual parameter
depends on how the command procedure is programmed". If you have selected a
graph then you can call its procedures, or send it messages if you want to
be object-oriented about it.

B