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From: kasper@rakau.cosc.canterbury.ac.nz (Kasper Osterbye)
Newsgroups: comp.lang.beta
Subject: Re: Redefinition of attributes in BETA (Q)
Date: 13 Oct 1996 22:32:26 GMT
Organization: University of Canterbury
Lines: 43
Message-ID: <KASPER.96Oct14113226@rakau.cosc.canterbury.ac.nz>
References: <325B9F88.1C10@informatik.uni-stuttgart.de>
NNTP-Posting-Host: 132.181.12.84
In-reply-to: Bernd Holzmueller's message of Wed, 09 Oct 1996 14:50:16 +0200

> From: Bernd Holzmueller <holzmuel@informatik.uni-stuttgart.de>
> Newsgroups: comp.lang.beta
> Date: Wed, 09 Oct 1996 14:50:16 +0200
> Organization: University of Stuttgart
> 
> Is it possible to give a completely new attribute definition in a
> subpattern for a non-virtual attribute? And, if so, does the subpattern
> then contain both attribute definitions (like in SIMULA)? And, if so,
> how can one access the overriden attribute? 
> 
> E.g., is it allowed to write
> 
>   	V: (# A: @Integer; #)
> 
>   	W: V (# A: @Real; #)
> 
> and does then the W pattern look like 
> 
> 	(# A: @Integer; A: @Real; #) ?

You got it all right!

From within W you might refere to the A in V as "this(V).A".

If A in V is virtual, you can also override it as in

   	V: (# A:<SomeThing #)
 
   	W: V (# A: SomeOtherThing; #)

This will just ignore that A is virtual, thus 

myW : @W
do myW.A 

myA will refere to the A in W, and completely ignore that there was a
A in V. The compiler will not warn about this, as it is quite ok, so
this can be a good source of confusion if you really just forgot a
colon eg. you wanted to write V(# A::(#...#) #), but wrote 
V(# A:(# ... #) #).

Regards,
	Kasper