• Corpus ID: 17327906

On the type ex tens ions of Oberon-2

@inproceedings{Nigro1993OnTT,
  title={On the type ex tens ions of Oberon-2},
  author={Libero Nigro},
  year={1993}
}

• L. Nigro
• Published 1993
• Chemistry

I n t r o d u c t i o n O b e r o n [Wir92] is t he n a m e b o t h of a n innovat ive Opera t ing S y s t e m [Gut90, Rei911 and of the language [Rei92] which w a s used , to a large extent , in the deve lopment of the s y s t e m and wh ich a l lows p r o g r a m m e r s to f u r t h e r e x t e n d t h e s y s t e m in a h igh ly i n t eg ra t ed a n d u n i f o r m way. The luc id i ty and m i n i m a l i t y of the O b e r o n des ign are impres s ive a n d are a n au tho r i t a t i ve c lear indica t ion of how complex sof tware s y s t e m s can be bui l t wi thout having j u s t to add layers to layers of sof tware the b a d c o m m o n t rend in t h e s o f t w a r e a r e a t o d a y wi th t h e i n e s c a p a b l e c o n s e q u e n c e of c r e a t i n g dupl ica t ion of func t ions or, worse , of hiding f u n d a m e n t a l lower func t ions . This s i tua t ion in t u r n leads to big sof tware packages whose ha rdware r e q u i r e m e n t s c an even exceed the capab i l i t i e s of m o d e r n power fu l p e r s o n a l works t a t i ons . The O b e r o n sys t em, ins tead , r e s t s u p o n a few b a s i c p r inc ip les a m o n g w h i c h o b j e c t o r i e n t a t i o n t h r o u g h t h e c o n c e p t s of r ecord type ex tens ions [Wir871. Dur ing the imp lemen ta t ion of the Opera t ing Sys tem, the O b e r o n l anguage w a s t u n e d to b e t t e r serve to i ts end goal and Oberon -2 ref lects t he l a t e s t l a n g u a g e redefini t ion. It isn ' t the pu rpose of th is shor t no te to provide a tu tor ia l of Oberon-2 . The in te res ted reader is r e f e r r ed to t h e r e l e v a n t b i b l i o g r a p h y IWir88a, Wir88b, Rei921. The objective of this no t e is to p o i n t o u t t h e w a y O b e r o n 2 s u p p o r t s t he bu i ld ing of type h ie ra rch ies , which , be ing b a s e d on s t rong in fo rma t ion hiding, c a n be too restr ict ive in the pract ical c o n s t r u c t i o n of i n h e r i t a n c e b a s e d t ype hierarchies . A m i n o r ex tens ion is sugges t ed w h i c h i m p r o v e s t h e e f f e c t i v e n e s s of t he l a n g u a g e . In t he fol lowing, t he O b e r o n s y s t e m is a s s u m e d to be available on one of the poss ib le p l a t fo rms wh ich inc lude Sun , PC, Macin tosh and so forth. M o d u l e s and a l ~ t r a e t data t y p e s P r o g r a m m i n g in O b e r o n 2 re l ies u p o n the f u n d a m e n t a l i s s u e s of i n t roduc ing , u s i n g a n d ex tending a b s t r a c t da t a t y p e s (adt). An ad t normal ly t akes the shape of a record type def ined in a m o d u l e t he b a s i c l anguage cons t ruc t which can be compi led as a unit . A m o d u l e i n t r o d u c e s a g loba l s c o p e w h i c h a f f ec t s t he v i s ib i l i ty of t he en t i t i e s t h e m o d u l e s p e c i f i e s a n d w h i c h c a n b e select ively expor ted . The following s h o w s a m o d u l e C o u n t e r s w h i c h p rov ides a s imple