LENS: Embeddable scripting for .NET

Welcome to the homepage for LENS embeddable compiler!

LENS stands for "Language for Embeddable .NET Scripting".

A few examples of the syntax

A basic script:

let a = 1
let b = 2
print "the result is: {0}" (a + b)

A loop:

for x in 10..0 do
    println "{0}..." x

println "blastoff!"

LINQ queries:

let squareSum = 1.to 100
    |> Where x -> x.even()
    |> Select x -> x ** 2
    |> Sum ()

Function declaration:

using System.Drawing

pure fun dist:double (p1:Point p2:Point) ->
    let x = p1.X - p2.X
    let y = p1.Y - p2.Y
    Math::Sqrt (x ** 2 + y ** 2)

let pA = new Point 1 2
let pB = new Point 10 20
print "The distance is: {0}" (dist pA pB)

Custom data structures:

record Store
    Name : string
    Stock : int

let stores = new [
    new Store "A" 10
    new Store "B" 42
    new Store "C" 5
]

for s in stores.OrderByDescending (x-> x.Stock) do
    println "Store {0} contains has {1} products in stock" s.Name s.Stock

Partial application and function composition:

let multiplier = (x:int y:int) -> x * y
let inv = (a:string b:string) -> b + a
let doubler = multiplier 2 _

// compose functions together
let invParse = inv :> int::Parse :> doubler :> (x -> println x)

invParse "1" "2" // 42

Pattern matching:

fun desribe:string (arr:object[]) ->
    match arr with
        case [] then "empty array"
        case [x:int] when x < 10 then fmt "array with 1 small int ({0})" x
        case [x] then "array with 1 item"
        case [x; y] then "array with 2 items"
        case [x; y; ...z] then fmt "array with {0}, {1} and {2} more items" x y z.Length

Why another language?

LENS provides an easy way to compile and execute a script within your application, and manages the interconnection between the app and the script. The language has a light, conscise, and type-safe syntax with rich functional features.

Oh really?

Why yes indeed! Here's a snippet that shows how to embed the compiler into your application:

try
{
    var x = 21;
    var y = 2;
    var result = 0;

    var cp = new LensCompiler();
    cp.RegisterProperty("x", () => x);
    cp.RegisterProperty("y", () => y);
    cp.RegisterProperty("res", () => result, r => result = r);

    var source = "res = x * y";
    var compiled = cp.Compile(source);
    compiled.Run();

    Console.WriteLine("The result is {0}", result);
}
catch(LensCompilerException e)
{
    Console.WriteLine("An error has occured: {0}", e.FullMessage);
}

The code above creates the compiler and registers local variables x, y, and result in the script. The body of the script is compiled into a native .NET object that can be invoked several times without recompilation. Finally, the result of the expression is printed out - and guess what the result is!

Why might one need an embeddable scripting language?

There are many cases in which your application can benefit from an embeddable scripting language:

• Tasks automation

  Write scripts to execute tasks automatically within the application, like processing a batch of images in a graphical editor, backing up databases.

• Formulas support

  Enable Excel-like formulas in your application, with functions and all kinds of cool features.

• Easy tweaking

  Embeddable scripting is a much more powerful alternative to config files. Scripts can contain some logic which can be altered without recompiling the entire application. Especially useful in game engines!

What features does the language support?

The compiler already supports the following features:

• Full access to any .NET types and assemblies referenced by your host project
• Import of types, methods and even local variables from host into the script
• Declaration of records and functions inside the script
• Local type inference
• Anonymous functions with closures
• Extension methods and LINQ
• Overloaded operators support
• Partial function application and function composition
• Pattern matching (with awesome regex support)
• Automatic memoization support
• Shorthand operators
• Basic optimizations like constant unrolling
• Safe mode: certain types or namespaces can be disabled for security reasons

Please refer to the Wiki for the complete list of features.

Contributions are always welcome - especially if you would like to help create a text editor with code suggestions and syntax highlighting!

What NOT to expect

Being designed as an embeddable language, LENS does not support some features that are better implemented in the language of the host application. Here is a list of features that you will not see any time soon:

• Unsafe code with pointers
• Checked / unchecked semantics
• Multiple source files support
• Declarations of classes or interfaces
• Access restrictions (private / public, etc)

Supporting documentation

• How to publish NuGet package