Advogato: Language Design

Here is a simple example of Suneido code:

/* 
multi-line comment 
*/ 
calc = function (x, y = 0, dbl = False) 
    { 
    sum = x + y // single line comment 
    if (dbl is True) 
        sum *= 2 
    return "result is " $ sum 
    } 
calc(123) => "result is 123" 
calc(123, 456) => "result is 579" 
calc(10, dbl:, y: 5) => "result is 30" 
calc("123") => "result is 123"

Notice:

C/C++/Java style comments, either /* */ or //
Functions are declared using the keyword ``function''
Functions (and classes) are "values" - they can be assigned to variables etc.
Function arguments can have default values
Function calls can use named arguments, in which case order is not significant. If a value isn't supplied for named argument, it defaults to True.
Semicolons are not required (but are allowed)
Variables do not need to be declared, and may contain any type - i.e. Suneido is a dynamically typed language
is, isnt, not, and, or are normally used but ==, !=, !, &&, || are allowed
Suneido includes all of the C/C++ operators, including assignment operators (e.g. *=), increment, decrement, and bit manipulation, and adds regular expression operators ~~ and !~
Automatic conversions between numbers and strings.
String concatenation is done with the "$" operator, not by overloading "+". This makes "123" + 456 and 123 $ "456" unambiguous.
Suneido includes the same control statements as C/C++ if-else, while, do-while, switch, but unlike C/C++ conditions must evaluate to true or false or you'll get an error. Switches are also slightly different - you can't "fall through" cases, and cases allow multiple expressions rather than integer constants. There is also a "foreach" statement (see below).

Functions can take variable numbers of arguments:

max = function (@args) 
    { 
    max = args[0] // will throw exception if no args 
    foreach (value x in args) 
        if (x > max) 
            max = x 
    return max 
    }
max(3, 6, 2, 5) => 6 
max("joe", "fred", "sam", "mike") => "sam"

@args puts all the arguments into a Suneido "object" (see below). foreach iterates through all the values in the object, in this case all the arguments.

You can also pass a pre-assembled set of arguments, using @.

ages = #(23, 67, 34, 19) 
max(@ages) => 67

Memory is garbage collected - there is no explicit allocation or freeing. However, finalization is not supported yet, so resources (e.g. Windows handles) must be explicitly released.

The basic data types in Suneido include: boolean (True and False), number, string, and object.

Suneido has a single numeric type - decimal floating point. Keeping numbers in decimal rather than binary allows exact representation of decimals, e.g. for amounts of money. Numbers have 16 digits of precision with an exponent range of plus or minus 127.

Strings are not null terminated so they can store arbitrary binary data as well as text. Strings are immutable i.e. there is no way to "modify" an existing string. (Objects are the only basic data type that is mutable.) This means that substring (s.Substr(i,n)) does not need to do any copying - it just creates a new string that points to part of the old one. For speed, concatenation is "lazy"; it creates a linked list of string segments, which are automatically combined when a single string is required. This greatly reduces the amount of allocation and copying required to manipulate strings.

Suneido could be called a "pure" object-oriented language in the sense that all values (including literals) are "objects" that can have methods. For example:

"hello world".Substr(3,2) => "lo"
97.Chr() => "a"

However, unlike some object-oriented languages such as Smalltalk or Java, Suneido has standalone functions as well as methods in classes.

User defined methods can be added to the built-in classes by creating methods in specially named classes: Numbers, Strings, Dates, Objects, etc.

Suneido has only two "scopes", global and local. Global names must be capitalized i.e. start with an upper case letter. Globals are either builtin (to the executable) or user defined in libraries in the database. Global names are not variables - they cannot be assigned to by code. Names that start with a lower case letter are local to a single function. Currently there are no packages or modules with separate namespaces.

Like Java, Suneido compiles to a stack oriented "byte code" which is then interpreted. For example:

function (x) { return x * 100 }.Disasm()
=>  push auto x
    push literal 100
    *
    return

Linking is done dynamically at run time. This means there are no restrictions on compiling code with calls to undefined functions or inheriting from undefined base classes. Of course, if you try to actually access something undefined, you'll get a run time error.

Objects

Suneido has a single "universal" container type - objects. Unlike other languages like Python or Ruby, you don't have to worry about what type of container to use. Objects can be used as vectors (single dimensional arrays) or as "maps" or both at the same time. Internally, objects have a vector part and a hash map part. Classes and instances are implemented as objects containing methods and data members.

x = Object() 
for (i = 0; i < 6; ++i) 
    x[i] = i // access as a vector 
x.Add("six") // same as x[6] = "six"
x => #(0, 1, 2, 3, 4, 5, "six")
x = Object(name: "fred", age: 25) 
x.married = True
x => #(name: "fred", age: 25, married: True) 
x.name => "fred"
m = "age" 
x[m] => 25 // same as x.age

Exceptions

Suneido has exception handling similar to C++ or Java, with try, catch, and throw. However, Suneido exceptions are strings rather than class instances.

try
    ...
catch (exception)
    ...

The catch portion is optional if you simply want to ignore exceptions:

try Database("destroy mytable")

An uncaught exception calls a Handler function - defined in the standard library as the debugger.

You can throw your own exceptions:

if (x < 0) 
    throw "square root: invalid negative argument: " $ x

Blocks

Smalltalk style "blocks" are a recent addition to Suneido. Basically, a block is a section of code within a function, that can be called like a function, but that operates within the context of the function call that created it (i.e. shares its local variables).

Blocks can be used to implement user defined "control constructs". (In Smalltalk, all control constructs are implemented with blocks.) For example, you could implement your own version of "foreach":

for_each = function (list, block)
    {
    for (i = 0; i < list.Size(); ++i)
        block(list[i])
    }
list = #(12, 34, 56)
for_each(list)
    { |x| Print(x) }

 => 12
    34
    56

Suneido treats a block immediately following a function call as an additional argument.

Blocks can also be used to execute sections of code in specific "contexts". For example, the Catch function traps exceptions and returns them. (This is useful in unit tests to verify that expected exceptions occur.)

catcher = function (block)
    {
    try
        return block()
    catch (x)
        return x
    }
catcher( { xyz } ) => "unitialized variable: xyz"

But the interesting part is that a block can outlive the function call that created it, and when it does so, it keeps its context (set of local variables). For example:

make_counter = function (next)
    { return { next++ } }
counter = make_counter(10)
Print(counter())
Print(counter())
Print(counter())
=>  10
    11
    12

In this example, make_counter returns a block. The block returns next++. You see this type of code in Lisp / Scheme.

Classes

Classes are read-only objects containing methods (functions) and members (data). For example:

counter = class
    {
    New(start = 0)
        { .count = start }
    Next()
        { return .count++ }
    }
ctr = new counter
Print(ctr.Next())
Print(ctr.Next())
Print(ctr.Next())
=>  0
    1
    2

Within a method, the special name "this" refers to the current object. So members and methods of the current object can be referred to as "this.name" but this is normally shortened to simply ".name".

Member / method names are public if they start with an upper case letter and private if they start with a lower case letter. Private names can only be accessed by methods of the class. In the above example, "Next" is a public method and "count" is a private member.

New is the constructor. (C++ and Java use the name of the class instead of "New", but this wouldn't work for Suneido because it allows "anonymous" classes i.e. with no name.) Base class New's are automatically called first. You can supply arguments to base class constructors by making the first statement of New a call to "super". (Similar to Java.)

class
    {
    New(x, y, z)
        {
        super(x, y)
        ...

"super" can also be used to call base class versions of methods:

mystack = class : Stack
    {
    Push(x)
        {
        ...
        super.Push(x)
        ...
        }

Normally, "calling" a class is the same as creating an instance. (This can be changed by defining a method called "CallClass".) So the following are equivalent:

ctr = counter(5)
ctr = new counter(5)

Any method in Suneido can be a "class" or "static" method, providing it doesn't need to set any members. If a method is called on a class rather than an instance, "this" will be the class itself, and therefore read- only.

If a nonexistent member is accessed, Suneido will call a method with the same name with no arguments, if present. This allows you to change a data member to a method without having to alter code that uses it. (Bertrand Meyer calls this "Uniform Access" - a client should be able to access a property of an object using a single notation, whether the property is implemented by memory or computation.)

If a nonexistent method is called, Suneido will call a method called "Default" if it is present. This can be used to implement delegation, or to handle methods that are not pre-determined.

Since classes and instances are objects, and have methods to get their base class, it is easy for code to inspect methods and members. Java calls this "reflection".

Stack.Members()
=> #("Pop", "Top", "Push")

Object syntax can also be used to access methods or members "indirectly":

m = "Add"
ob[m](value) // equivalent to ob.Add(value)

"Missing" Features

no declarations
no preprocessor i.e. #define or #include
no enums
no multiple inheritance (although this may be added)
no operator overloading
no goto
no explicit pointers
no explicit free'ing of memory
no separate module or package namespaces
no non-local returns from blocks
no "protected" members / methods (just private and public)
no "static" class data members (just class methods)

Summary

The Suneido language is:

small, simple
object-oriented
dynamically typed - no declarations
functionally similar to Smalltalk
familiar to anyone who has programmed in C, C++, Java etc.
safe - automatic memory management (garbage collection) and no pointers

Language Design

Posted 9 Dec 2000 at 22:43 UTC by apm

PS., posted 9 Dec 2000 at 22:47 UTC by apm » (Journeyer)

let's see, posted 9 Dec 2000 at 23:12 UTC by cmm » (Journeyer)

Indeed., posted 9 Dec 2000 at 23:33 UTC by egnor » (Journeyer)

Toy languages, posted 10 Dec 2000 at 01:16 UTC by raph » (Master)

Comments, posted 10 Dec 2000 at 04:16 UTC by nymia » (Master)

Language mixing, posted 10 Dec 2000 at 04:29 UTC by hp » (Master)

Intermediate languages, posted 10 Dec 2000 at 05:28 UTC by egnor » (Journeyer)

Bytecode and virtual machine design is important, posted 10 Dec 2000 at 06:43 UTC by pphaneuf » (Journeyer)

IL Design -- The Ultimate Solution, posted 10 Dec 2000 at 12:09 UTC by moshez » (Master)

Scheme as an IL, posted 10 Dec 2000 at 13:20 UTC by cmm » (Journeyer)

Re: Toys Languages, posted 10 Dec 2000 at 14:43 UTC by hadess » (Master)

comments, posted 10 Dec 2000 at 14:49 UTC by apm » (Journeyer)

UNWIND-PROTECT ?, posted 10 Dec 2000 at 16:43 UTC by dan » (Master)

re. unwind-protect / finally, posted 10 Dec 2000 at 17:29 UTC by apm » (Journeyer)

"finally" considered harmful, posted 10 Dec 2000 at 23:30 UTC by ncm » (Master)

huh?, posted 11 Dec 2000 at 00:31 UTC by cmm » (Journeyer)

Uniform Access, posted 11 Dec 2000 at 05:19 UTC by Dacta » (Journeyer)

re. Uniform Access, posted 11 Dec 2000 at 15:14 UTC by apm » (Journeyer)

re. "finally", posted 11 Dec 2000 at 15:33 UTC by apm » (Journeyer)

Re: Uniform Access, posted 11 Dec 2000 at 16:07 UTC by ingvar » (Master)

finalize considered harmful!, posted 12 Dec 2000 at 09:09 UTC by taj » (Master)

Looks kind of similiar to elastiC, posted 14 Dec 2000 at 13:55 UTC by davidw » (Master)

Re:finalize considered harmful! (and finally considered harmful), posted 15 Dec 2000 at 00:56 UTC by Dacta » (Journeyer)

Why I don't like `finally', posted 20 Dec 2000 at 02:06 UTC by dan » (Master)