TweetFollow Us on Twitter

March 93 - An Introduction to BETA: A New Object-oriented Language

An Introduction to BETA: A New Object-oriented Language

Steve Mann

New object-oriented products are announced every day. Most of them are based on a familiar language such as C++, SmallTalk, or LISP / CLOS. New object-oriented languages are another matter. When was the last time you saw an announcement for a commercial-grade object-oriented language product? BETA is such a product.

Development on BETA started in 1976 as a joint venture between several universities in Norway, Denmark, and Finland. This is the same computer science community (often called the Scandinavian School of object-orientation) that in the early 1960s developed Simula, the first object-oriented language. Throughout its formative years, the BETA research has been supported by grants from many companies, including Apollo, Apple, and Hewlett Packard. After more than 15 years of research and development, Mjolner Informatics has released the first commercial BETA product.

AN OVERVIEW OF BETA

BETA is a completely new language with a design heavily influenced by its object-oriented predecessors, especially Simula. It is strongly typed like C++, with most type checking being done at compile time. The language design is based on a powerful abstraction mechanism called a pattern. The syntax for a pattern is:
<Pattern Name> :
    (#  <Attribute 1> ;
        <Attribute 2> ;
            .
        <Attribute N> ;

    Enter <Input list>
    Do <Imperatives>
    Exit <Output list>
    #);

Attributes can be many things-the most common are object declarations and methods specific to the pattern being defined. The Enter statement lists the values passed to the Do section, Exit lists the values output from the Do section. The Do section contains imperative (executable) statements that perform actions. All the syntactic elements of a pattern are optional.

There are several types of patterns, including classes, procedures, functions, coroutines, processes, and exceptions. There are also three types of pattern derivatives:

  • subpatterns (like subclasses but more powerful),
  • virtual patterns (like C++ virtual procedures), and
  • pattern variables (variables that can be assigned any legal pattern value).

You can create any of these three derivatives from any of BETA's pattern types, making BETA a very orthogonal language. For instance, using subpatterns, you can create a hierarchy of procedures, functions, coroutines, processes, or exceptions, where all the subpatterns inherit attributes from their superpatterns. You can also define virtual classes, virtual procedures, virtual functions, and so on . Table 1 lists all the possible combinations of pattern derivatives and types.

Other important BETA features include:

  • class-less objects for one-of-a-kind object definitions;
  • direct and reference (pointer-based) attributes allowing the modeling of complex relationships;
  • block structures similar to Algol, allowing nested structures with local and global scopes for all patterns.

SAMPLE PROGRAMS

Here is a simple class pattern that defines a bank account object. It has three attributes-balance (a declaration using a predefined class pattern called integer), Deposit (a procedure pattern), and Withdraw (another procedure pattern).
Account :  (* a simple bank account class pattern *)   
    (#  balance : @ integer;        (* bank account balance *)

        Deposit :       (* add 'amount' to balance *) 
            (#  amount : @ integer          (* local declaration *)
            enter amount                    (* input list *)
            do balance + amount -> balance   (* action *)
            exit balance                        (* output list *)
            #); 
        Withdraw :      (* subtract 'amount' from balance *)
            (#  amount : @ integer  
            enter amount    
            do balance - amount -> balance
            exit amount     
            #); 
    #); 

Note that:

  • Asterick/parens ('(*' and '*)') are used to enclose comments.
  • A colon (':') indicates a declaration.
  • An @ sign indicates the name of an object type.
  • Integer is a predefined BETA basic pattern (the other basic patterns are real, boolean, and char, plus there is a predefined text pattern that works much like strings).
  • Imperative statements always read left to right.

According to BETA terminology, both Deposit and Withdraw are procedure (not function) patterns. BETA procedures and functions both can have input and output lists. A BETA function computes a return value using only the input values, causing no side effects (a procedure may cause side effects).

The preceding sample is simply a class definition pattern with attributes (balance) and methods (Deposit and Withdraw). In order to create a complete BETA program, we need more, such as some declarations to create real account objects, and some imperatives to perform actions on those accounts:

(# (* a pattern with no name *)
    Account : (*  a pattern declaration within the unnamed pattern *)
        (#  acct_balance : @ integer;
            Deposit :                
                (#  amount : @ integer  
                enter amount
                do acct_balance + amount -> acct_balance
                exit balance    
                #); 
            Withdraw :      
                (#  amount : @ integer  
                enter amount    
                do acct_balance - amount -> acct_balance
                exit amount     
                #); 
            Balance :
                (#
                exit acct_balance
                #)
        #); 
    A : @ Account;              
    cash_on_hand, balance : @ integer;  

do  100 -> &A.Deposit;               
    250 -> &A.Deposit;               
    75  -> &A.Withdraw -> cash_on_hand;   (* $75 on hand *)
    &A.Balance -> balance;                (* $275 balance *)
#)

In BETA the symbol '&' means new; the expression &account.Deposit means "create a new instance of the pattern account.Deposit and execute it". This is basically the same as invoking a procedure. Note that the finished program, the primary object definition (Account), and the methods that operate on that account (Deposit, Withdraw, and Balance) are all patterns. This use of a single syntactic element to define everything and execute operations gives BETA much of its power and flexibility.

REFERENCE ATTRIBUTES

BETA allows you to define both static and dynamic reference attributes. The previous sample programs all have examples of static object references such as
A : @ Account;             
cash_on_hand, balance : @ integer;

Static objects are also called part objects (or part references) in BETA because the declared objects are a permanent part of the objects containing their declarations.

BETA also lets you define object references that denote different objects at different points in time (much like pointers). An example of a dynamic reference is

A : ^Account ;

The initial value of a dynamic reference is NONE (trying to reference an object attribute using a NONE pointer causes a runtime error). If we define an account using

A1 : Account ;

we can assign A1 to A using the statement

A1[] -> A[] ;

It is also possible to create objects dynamically by invoking their pattern as an executable statement. For instance, the statement

&Account[]

creates a new instance of an Account and returns a reference to that account. If we declare a reference object using

A1 : ^Account;

the following statement is valid:

&Account[] -> A1[];

The difference between &Account and &Account[] is important. The first means "generate an instance of Account and execute it"; the second means "generate a new instance of Account without executing it and return a reference to it".

OTHER BETA SYNTACTIC ELEMENTS

When presenting a new language, there is always a certain amount of rote presentation to cover the basic syntax needed to create programs in that language. This section covers some of the more recognizable parts of BETA, including predefined basic patterns and attributes, arrays, assignment statements (evaluations), and control statements.

Basic Patterns

BETA has four predefined basic patterns : integer, real, boolean, and char. The default values and standard operators for BETA's basic patterns are shown in Table 2. In addition, BETA has a standard set of relational operators. Chars are ordered from 0 to 255, and false is less than true.

One unusual restriction that BETA has is that it is not possible to declare dynamic references to instances of these four basic patterns. Apparently this restriction is primarily for efficiency reasons.

Repetitions

BETA arrays (called repetitions) are defined using one of these two forms:
<Name>: [size] @<Type> ;       (* static repetition *)
<Name>: [size] ^<Type> ;        (* dynamic repetition *)

Array indices range from one to <Name>.range (range is an intrinsic attribute of all array objects). You can dynamically resize arrays using the extend attribute, which adds elements to an array. You can reallocate an array, initializing all the elements to the default value for the array object type. You can also assign array slices (or parts of an array).

Here are some array examples:

A1, A2 : [10] @integer;    (* integer arrays A1[1]-A1[10],
                              A2[1]-A2[10] *)
1050 -> A1.[1];         (* assignment *)
10 -> A1.extend;        (* resize A2 to 20 elements *)
25 -> A2.new;           (* resize and reinitialize A2 *)
A1 [1:5] -> A2 [10];    (* slice assignment *)

There is also a special repetition pattern called text which is derived from a string pattern. It is a character array, subject to all normal array operations, with additional predefined patterns for string manipulation.

For Statement

The BETA for statement is straightforward. It has the following form:
(for <Index>: <Range> repeat <Imperative-list> for)

<Index> is an integer object declared locally within the scope of the for statement. It cannot be changed within the loop. The index always starts at one and increments by one. A pattern with a for loop might look like

(#     sum: @ integer;
    V : [100] @ integer     (* integer array *)
do  (for i : V.range repeat i -> V [i] for)
    0 -> sum;
    (for i : V.range repeat sum + v [i] -> sum for)
#)

It is possible to overcome the limitations of the for index structure (integer indices which always start at one and increment by one) using other patterns. That capability is not explored in this introductory article.

If Statement

The BETA if statement is an unusual combination of a traditional if statement and a case statement. Its form is
(if E0
    // E1 then I1
    // E2 then I2
        . . .
    //En then In
    else I
if)

E1 . . . En are evaluations and I1 . . . In are imperatives. The else clause is optional. Here's an example of a simple if statement:

(if x
    // 17 then . . .
    // 33 then . . .
    // y+3 then . . .
    else
if)

A boolean evaluation (albeit an awkward one) might be written

(if (x > 0) and (y < 0)
    // True then . . .
    // False then . . .
if)

Evaluations

BETA evaluation (assignment) statements are very flexible. You can define multiple assignment statements such as
   3 -> I -> J

You can also combine multiple assignments with pattern executions and enter and exit redirection like in this program:

   (#  Power :     (* compute X^n where n > 0 *)
        (#  X, Y : @ real; n : @ integer;
        enter (X, n) 
        do  1 -> Y;
            (for i : n repeat Y * X -> Y for)
        exit Y
        #)

        Reciproc :  (* compute (Q, 1/Q) *)
        (# Q, R : @ real;
        enter Q
        do  (if (Q // 0) then 0 -> R
            else (1 div Q) -> R
            if )
        exit (Q, R)
        #);
    A, B : @ real;
    do  (3.14, 2) -> &Power -> &Reciproc -> (A, B);
        (* A = 3.14 ^ 2, B = 1/A *)
    #)

THE MJOLNER BETA SYSTEM

So far I have described the more basic elements of the BETA language. There are many advanced capabilities, such as subpatterns and virtual patterns, exception handling, and concurrency, that really show off BETA's power as an object-oriented language and the depth of its design. I''ll cover these topics in a future article.

The Mjolner BETA System, created by several of the language's original designers, is currently the only commercial implementation of a BETA development environment. The Mjolner BETA System includes:

  • native code generation,
  • automatic garbage collection and storage management,
  • separate compilation of program fragments with automatic dependency analysis,
  • interfaces to C and assembly language modules (and Pascal on the Mac),
  • persistent objects, although not a full-blown object-oriented database (a complete OODB is expected by late 1993),
  • basic patterns for simple data types,
  • a set of container patterns for more complex data structures (including sets, has tables, stacks, queues, and lists),
  • stream patterns for text and file handling,
  • process management and concurrency control patterns, and
  • application frameworks for X Windows, Motif, and the Macintosh Toolbox.

As if that weren't enough, Mjolner also sells a variety of additional tools including a modifiable Hyper Structure Editor, a metaprogramming system, a BETA CASE Tool (Unix only), and a source-level debugger (Unix only). In the coming months we hope to present an overview of BETA's advanced features, a comprehensive review of Mjolner's BETA System and tools, and advanced programming examples. Let us know if there are specific topics you would like addressed. -

MADA is pleased to announce that as we were going to press with this issue, Mjolner selected MADA as their exclusive US and Canada distributor for the Macintosh version of BETA. We are also carrying the reset of the Mjolner BETA product line. See page 67 for more details.

In addition, a demo version of the Mjolner BETA System is available on MADA's "Five Years of Objects" CD-ROM.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

calibre 2.69.0 - Complete e-book library...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital librarian... Read more
Evernote 6.9.1 - Create searchable notes...
Evernote allows you to easily capture information in any environment using whatever device or platform you find most convenient, and makes this information accessible and searchable at anytime, from... Read more
jAlbum Pro 13.5 - Organize your digital...
jAlbum Pro has all the features you love in jAlbum, but comes with a commercial license. You can create gorgeous custom photo galleries for the Web without writing a line of code! Beginner-friendly... Read more
jAlbum 13.5 - Create custom photo galler...
With jAlbum, you can create gorgeous custom photo galleries for the Web without writing a line of code! Beginner-friendly, with pro results - Simply drag and drop photos into groups, choose a design... Read more
Google Chrome 53.0.2785.143 - Modern and...
Google Chrome is a Web browser by Google, created to be a modern platform for Web pages and applications. It utilizes very fast loading of Web pages and has a V8 engine, which is a custom built... Read more
Chromium 53.0.2785.143 - Fast and stable...
Chromium is an open-source browser project that aims to build a safer, faster, and more stable way for all Internet users to experience the web. Version 53.0.2785.143: [Security Fix] High CVE-2016-... Read more
QuickBooks 2015 16.1.7.1524 R8 - Financi...
Save 20% on QuickBooks Pro for Mac today through this special discount link QuickBooks 2015 helps you manage your business easily and efficiently. Organize your finances all in one place, track... Read more
Sierra Cache Cleaner 11.0.1 - Clear cach...
Sierra Cache Cleaner is an award-winning general purpose tool for macOS X. SCC makes system maintenance simple with an easy point-and-click interface to many macOS X functions. Novice and expert... Read more
Default Folder X 5.0.7 - Enhances Open a...
Default Folder X attaches a toolbar to the right side of the Open and Save dialogs in any OS X-native application. The toolbar gives you fast access to various folders and commands. You just click on... Read more
Safari Technology Preview 10.1 - The new...
Safari Technology Preview contains the most recent additions and improvements to WebKit and the latest advances in Safari web technologies. And once installed, you will receive notifications of... Read more

Pumped BMX 3: Beginner tips and tricks
There’s a whole lot more to Pumped BMX 3 than meets the eye. Your goal is to perform a wide array of sweet flips and tricks, but that’s easier said than done. It takes well practiced timing and coordination, and the game doesn’t really explain that... | Read more »
Cybird’s latest release - BFB Champions...
Launched in the UK in early September, BFB Champions’ newest update is loaded with great new features, and looks set to outshine the original version by taking it out of soft launch and giving it a new lease of life. | Read more »
3 apps to boost your focus
As someone who works from home, my workspace is a minefield of distraction. Cats, tasty snacks, the wind blowing past my window, that cleaning that I suddenly can’t put off any longer. If I let distraction takes its course, I find that soon half... | Read more »
Pumped BMX 3 (Games)
Pumped BMX 3 1.0 Device: iOS Universal Category: Games Price: $3.99, Version: 1.0 (iTunes) Description: The final instalment of the smash hit #1 rated BMX game is here! Following on from the insane success of Pumped BMX 2, Pumped 3... | Read more »
4 games like Burly Men at Sea to inspire...
Burly Men at Sea is out today and it looks a treat. It tells the tale of three Scandinavian fishermen who leave the humdrum of their daily lives to go exploring. It’s a beautiful folksy story that unfurls as you interact with the environment... | Read more »
3 reasons you need to play Kingdom: New...
Developed by a tag team of indie developers - Thomas "Noio" van den Berg and Marco "Licorice" Bancale - Kingdom is a vibrant medieval fantasy adventure that casts players as a king or queen who must expand their empire by exploring the vasts lands... | Read more »
JoyCity have launched a brand new King o...
Great news for all of you Game of Dice fans out there - JoyCity have just released a brand new limited edition pack with a really cool twist. The premise of Game of Dice is fairly straightforward, asking you to roll dice to navigate your way around... | Read more »
Burly Men at Sea (Games)
Burly Men at Sea 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Burly Men at Sea is a folktale about a trio of large, bearded fishermen who step away from the ordinary to seek adventure. | Read more »
3 tips for catching the gnarliest waves...
Like a wave breaking on the shore, Tidal Rider swept its way onto the App Store charts this week settling firmly in the top 10. It’s a one-touch high score-chaser in which you pull surfing stunts while dodging seagulls and collecting coins. The... | Read more »
The beginner's guide to destroying...
Age of Heroes: Conquest is 5th Planet Games’ all new turn-based multiplayer RPG, full of fantasy exploration, guild building, and treasure hunting. It’s pretty user-friendly as far as these games go, but when you really get down to it, you’ll find... | Read more »

Price Scanner via MacPrices.net

CAZE Annouces New Zero 5 Case for Jet Black i...
Hong Kong basd CAZE has announced Zero 5 case for iPhone 7/ 7 Plus, one of the world’s thinnest clear hard cases, measuring just 0.5 millimeters. CAZE has been producing and improving the Zero 5... Read more
Nest Egg Inventory App for iOS Offers Conven...
Campbell, California based Winprogger LLC has announced the release and immediate availability of Nest Egg – Inventory 4.1.22, an important update to their easy-to-use, yet comprehensive inventory... Read more
Factor4, LLC Launches Apple iOS and Android G...
Factor4, LLC, which offers gift and loyalty services to the SMB marketplace, has released free mobile applications that enable merchants to process via all Apple and Android devices. The Apple and... Read more
15-inch Retina MacBook Pros on sale for $200...
B&H Photo has 15″ Retina Apple MacBook Pros on sale for $200 off MSRP. Shipping is free, and B&H charges NY tax only: - 15″ 2.2GHz Retina MacBook Pro: $1799 $200 off MSRP - 15″ 2.5GHz Retina... Read more
Apple refurbished iMacs available for up to $...
Apple has Certified Refurbished 2015 21″ & 27″ iMacs available for up to $350 off MSRP. Apple’s one-year warranty is standard, and shipping is free. The following models are available: - 21″ 3.... Read more
Check Apple prices on any device with the iTr...
MacPrices is proud to offer readers a free iOS app (iPhones, iPads, & iPod touch) and Android app (Google Play and Amazon App Store) called iTracx, which allows you to glance at today’s lowest... Read more
Apple price trackers, updated continuously
Scan our Apple Price Trackers for the latest information on sales, bundles, and availability on systems from Apple’s authorized internet/catalog resellers. We update the trackers continuously: - 15″... Read more
Apple refurbished 2016 13-inch MacBook Airs a...
Apple has Certified Refurbished 2016 13″ MacBook Airs available starting at $849. An Apple one-year warranty is included with each MacBook, and shipping is free: - 2016 13″ 1.6GHz/8GB/128GB MacBook... Read more
1.4GHz Mac mini on sale for $449, save $50
Adorama has the 1.4GHz Mac mini on sale for $50 off MSRP including free shipping plus NY & NJ sales tax only: - 1.4GHz Mac mini (Apple sku# MGEM2LL/A): $449 $50 off MSRP To purchase a mini at... Read more
Apple refurbished 2015 13-inch MacBook Airs a...
Apple has Certified Refurbished 2015 13″ MacBook Airs available starting at $759. An Apple one-year warranty is included with each MacBook, and shipping is free: - 2015 13″ 1.6GHz/4GB/128GB MacBook... Read more

Jobs Board

*Apple* Retail - Multiple Positions- Akron,...
Job Description:SalesSpecialist - Retail Customer Service and SalesTransform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Hardware Design Validation Engineer - *Apple...
Changing the world is all in a day's work at Apple . If you love innovation, here's your chance to make a career of it. You'll work hard. But the job comes with more Read more
Systems Architecture Prototyping - *Apple*...
Changing the world is all in a day's work at Apple . If you love innovation, here's your chance to make a career of it. You'll work hard. But the job comes with more Read more
*Apple* Retail - Multiple Positions- South B...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Restaurant Manager (Neighborhood Captain) - A...
…in every aspect of daily operation. WHY YOU'LL LIKE IT: You'll be the Big Apple . You'll solve problems. You'll get to show your ability to handle the stress and Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.