AjSharp programming language: a C#-like dynamic language

During the creation of AjGenesis, my code generation project, I defined an interpreted language, named AjBasic, used to write templates and tasks for code generation process. Last year, I began to separate AjBasic implementation of AjGenesis core, and as a proof of concept, I wrote AjSharp, another interpreted language but with more C#-like syntax, using the same core interpreter that I wrote for AjBasic. The core machine was AjInterpreter. More info at:

AjSharp- a C Sharp-like interpreter, work in progress

Now, this year, I started a clean implementation, inside my AjCodeKatas Google Code. The core interpreter is now AjLanguage, and AjSharp is the language with a parser that relies on the core “virtual machine” to build and execute an abstract tree:

Current source code (under development) can be downloaded from:

http://code.google.com/p/ajcodekatas/source/browse/#svn/trunk/AjLanguage

Variables, expressions and commands

Variables are untyped, and are automatically declared when they are used:

a = 1;

b = 2;

These variables contain integer values, but they can be assigned to values of other types:

a = “one”;

b = “two”;

The common commands are supported:

if (k>0)

 return;

for (k=1; k<=10;

k++)

 sum = k+sum;

while

(j<10)

 DoProcess(j);

foreach (element in

elements)

 AddElement(element);

Conditional expressions can be any expression, not only boolean ones. See above, False value explanation.

Functions and Subroutines

This is the sintax to write down a factorial function:

function Factorial(n)

{

 if

(n<=1)

 return

1;

 return n * Factorial(n-1);

}

The word “sub” can be used to define subroutines.

Functions and subroutines are like any other values. They can be defined without name and assigned to variables:

Add1 = function (n) { return n+1; }

two = Add1(1);

function Apply(func,values)

{

 list = new

List();

 foreach (value in

values)

list.Add(func(value));

 return list;

}

numbers = new

List();

numbers.Add(1);

numbers.Add(2);

numbers.Add(3);

function Square(n) { return n*n; }

squared = Apply(Square, numbers);

squared2 = Apply(function (n) { return

n*n; }, numbers);

Native .NET objects

One of the design goals of AjLanguage core is to have access to .NET objects. They can be created using the new keyword:

ds = new System.Data.DataSet();

dinfo = new System.IO.DirectoryInfo(“.”);

foreach (fi in dinfo.GetFiles()) {

PrintLine(fi.FullName);

}

Dynamic objects

Dynamic objects can be created using the new keyword. A dynamic object accepts new members (variables and methods):

dynobj = new DynamicObject();

dynobj.FirstName = “Adam”;

dynobj.LastName = "Genesis”;

dynobj.Age =

800;

dynobj.FullName = function() { return FirstName + “ “ + LastName; }

Another notation:

dynobj = new { Name = “Adam”, Age = 800 };

Another notation:

dynobj = new { var FirstName = “Adam”; var LastName = “Genesis”; function

FullName() { return FirstName + “ “ + LastName; }

Dynamic objects are defined automatically, setting theirs properties:

Project.Database.Provider = “…”;

Project.Database.ConnectionString =

“…”;

creates Project dynamic object, with a Database property pointing to another dynamic object. It’s equivalent to:

Project = new DynamicObject();

Project.Database = new

DynamicObject();

Project.Database.Provider =

“…”;

Project.Database.ConnectionString = “…”;

An experiment: lists are defined automatically using Add method:

Project.Entities.Add(new { Name = “Customer”, Table = “dbo.Customers” });

it’s equivalent to:

Project = new DynamicObject();

Project.Entities = new

List();

Project.Entities.Add(new { Name = “Customer”, Table = “dbo.Customers”

});

Dynamic classes

A class can be defined using this sintax:

class Person {

 var FirstName;

 var

LastName;

 var Age;

 function

FullName {

 return FirstName + “ “ +

LastName;

 }

}

A new instance can be created as usual:

adam = new Person() { FirstName = “Adam”, LastName = “Genesis”, Age = 800 };

The instance is dynamic: new members can be attached to it, and methods could be redefined:

adam.FullName = function() { return “The “ + FirstName; };

You can create class as values:

Person = new DynamicClass();

but the interface to add members is still in flux.

Defined Classes

There are some predefined classes:

dynobj = new DynamicObject();

list = new List(); // implementing 

IList

dict= new Dictionary(); // implementing IDictionary

Primitive Functions

A few functions and subroutines are predefined:

Print(“Hello”);

PrintLine(“Hello World”);

There three predefined functions to execute and evaluate dinamic code:

Include("program.ajs");

Evaluate("k+1");

Execute("k=1;");

Include execute the commands in a file. Evaluate parses and evaluate an expression. And Execute compile and execute commands.

False value

Anything that is false, null, zero or empty string, is evaluated as false in conditional expression:

if (k)

 PrintLine(“true”);

else

PrintLine(“false”);

The above command prints “false” on execution, if k is zero or undefined. If a variable is undefined, any access to its member returns null, instead of a null exception:

if (Project.Database.ConnectionString)

PrintLine(“true”);

else

 PrintLine(“false”);

This command prints “false” again, if variable Project is undefined.

Arrays, List and Dictionaries

Native arrays can be defined with length:

firstprimes = new int[10];

or with values:

firstprimes = new int[] { 1, 2, 3, 5, 7, 9 };

A list is created if you need a dynamic array:

numbers[0] = “zero”;

numbers[1] = “one”;

numbers[2] =

“two”;

numbers[3] = “three”;

A dictionary is automatically created if the subindices are not numeric:

numbers[“one”] = 1;

numbers[“two”] = 2;

numbers[“three”] = 3;

If you need more feature, remember, you can use the native .NET framework.

Console interface

The project AjSharp.Console is a console application, where you can enter and execute AjSharp commands (not expressions):

No command to exit, yet. Just control+c in Windows.

Next steps

There are so many features I want to add. Partial list:

- AjBasic as another language over AjLanguage

- Generics support

- Template support (as in AjGenesis)

- Integrate to AjGenesis code generation

- Compile AST to Dynamic Language Runtime

Angel “Java” Lopez

http://www.ajlopez.com

http://twitter.com/ajlopez