Path: news.daimi.aau.dk!poe
From: Peter Andersen <Peter.Andersen@mjolner.dk>
Newsgroups: comp.lang.beta
Subject: Re: Constants in Beta
Date: 25 Apr 1995 15:54:33 GMT
Organization: DAIMI, Computer Science Dept. at Aarhus University
Lines: 71
Approved: mailtonews@daimi.aau.dk
Distribution: world
Message-ID: <3nj5vp$rum@belfort.daimi.aau.dk>
NNTP-Posting-Host: daimi.daimi.aau.dk

Baiss E. Magnusson writes:
> 
> Hello,
> 
> I see in the Beta demo programs a lot of lines where hard coded numeric
> values exist:
> 
> 	 clear : (# exit 6 #);
>    exit 130 #);                  (* resource id's for edit menu *)
>   
>    windowId : (# exit 128 #);    (* resource id of the application window
> *)
>    do (100, 100) -> position;
>    (300, 300) -> size;
> 
> Now in a real world application these numbers would exist in a separate
> <Defines> file and they would be reference by some constant name, or they
> would be calculated based upon some environmental setting.
> 
> This is accomplished in C with <#defines> so the above would be:
> #define  H_WINDOW 100
> ...
>  do (H_WINDOW, V_WINDOW) -> position;
>    (WINDOW_WIDTH, WINDOW_HEIGHT) -> size;
> etc.
> 
> What method in Beta would you use to replace all hard coded numeric
> values with substitute <macro> values?
> 

You could do it similarly:

H_WINDOW: (# exit 100 #);
V_WINDOW: (# exit 100 #);
...
do (H_WINDOW, V_WINDOW) -> position;
   (WINDOW_WIDTH, WINDOW_HEIGHT) -> size;

This method would force a recompilation each time you change the constants.
You could instead use virtual constants:

H_WINDOW:< IntegerValue(# do 100->value (* default *); INNER #);
V_WINDOW:< IntegerValue(# do 100->value (* default *); INNER #);

...

Then in some specialization you can override the default value (100)
by furtherbinding:

H_WINDOW::< (# do 200->value; INNER #);
V_WINDOW::< (# do 200->value; INNER #);

or final-binding:

H_WINDOW:: (# do 200->value #);
V_WINDOW:: (# do 200->value #);

Then you will only have to recompile the specialization to change the
size of all windows specified using H_WINDOW and V_WINDOW.

Sincerely,

Peter Andersen
_____________________________________________________________________________
Mjolner Informatics Aps                  Phone:   (+45) 86 20 20 00 ext. 2753
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Gustav Wieds Vej 10                      Fax:     (+45) 86 20 12 22
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_____________________________________________________________________________
			     BETA is better
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