Building DSLs On CLR and DLR (Microsoft.NET)

Building

on the CLR and DLR

MaximMoiseevmaxim.moiseev@gmail.com

moiseev

VitalyBaumvbaum@live.com

butaji

http://spbalt.net/

http://altdotnet.org

DOMAIN SPECIFIC LANGUAGES

The short annotation

Domain Specific Languages (DSLs)

are limited forms of computer language designed for a specific class of problems.

Martin Fowler

“(DSL) is a computer language that's

targeted to a particular kind of problem,

rather than a general purpose language

that's aimed at any kind of software

problem.”

Paul Graham

“*Lisp Programmers+ follow a principle

which could be called bottom-up design--

changing the language to suit the

problem.”

DSLS CLASSIFICATION

Types of DSL

Internal

• Written in host language

• Conventional use of subset of host language syntax

External

• Separate to host language

• Needs the compiler/interpreter to execute

Types of DSL

Internal

• Tied to base language

• Awkward with mainstream

External

• Lack of Symbolic Integration

• Complex parser/generator technologies

• Ignorant IDEs

• (language cacophony)

Types of DSL

Internal

• LINQ (C#)

• Monads (Haskell)

• Workflows (F#)

• Sequence expressions (F#)

• List comprehensions (Haskell, Python)

External

• Regexp

• SQL

• CSS

• Ant

• XSLT

Types of DSL

Log Activity

Clear Activity

Shutdown ActivityW

Graphical DSL

LANGUAGES

DSL Oriented .NET Languages

Smalltalk

Python

Smalltalk

Python

Boo DLRCLR

WHY SHOULD WE USE DSL?

The important advantages over a GPL

Why should we use DSL

• Domain-specific abstractions: a DSL provides pre-defined abstractions to directly represent concepts from the application domain. Consequently, domain experts themselves can understand, validate, modify, and often even develop DSL program

• Domain-specific concrete syntax: a DSL offers a natural notation for a given domain and avoids syntactic clutter that often results when using a GPL.

• Domain-specific error checking: a DSL enables building static analyzers that can find more errors than similar analyzers for a GPL and that can report the errors in language familiar to the domain expert.

• Domain-specific optimizations: a DSL creates opportunities for generating optimized code base on domain-specific knowledge, which is usually not available to a compiler for a GPL.

• Domain-specific tool support: a DSL creates opportunities to improve any tooling aspect of a development environment, including, editors, debuggers, version control, etc.; the domain-specific knowledge that is explicitly captured by a DSL can be used to provide more intelligent tool support for developers.

Why is DSL good?

Business Peoples and

“Rules”

Developers and their “Magic”

Read Writeand

director of finance for the client bank to edit, test,

and deploy the business rules of the system without any assistance from IT

Read Write

PATTERNS

DSL Building Patterns

Better code readability

• Fluent interfaces

• Extension methods

• LINQ

• Workflows

• Syntactic sugar

• AdHoc LINQ

Fluent interfaces

Expect

.On(…)

.Method(…)

.WithAnyArguments()

.Will(

Return.Value(…)

NMock mocking library usage

Fluent interfaces

Expect

.On(…)

.Method(…)

.WithAnyArguments()

.Will(

Return.Value(…)

public static Expect {…}

IRecieverSyntax

IMethodSyntax

IArgumentSyntax

IActionSyntax

IAction

Fluent interfaces

public class ExpectationBuilder:IReceiverSyntax,IMethodSyntax,IArgumentSyntax,IActionSyntax {…}

public IMethodSyntax On(…){// …return this;

}public IArgumentSyntax Method(…){

// …return this;

Combinations

today.at 3.pm

3.days.from_today at(3.pm)

Timespan Literals

print(50s) // 50 seconds

print(1d) // 1 day

print(2m) // 2 minutes

print(42ms) // 42 miliseconds

print("Tomorrow this time will be: ${date.Now + 1d}")

String interpolation

print("Now is ${date.Now}.")

print("Tomorrow will be ${date.Now + 1d}")

Extension methods

DateTime now = DateTime.Now;

TimeSpan span =

TimeSpan.FromDays(3);

DateTime res =

now + span;

DateTime res =

3.Days()

.From(

DateTime.Now

Extension methods

public static class MyExtensions {

public static TimeSpan Days(this int i) {return TimeSpan.FromDays(i);

public static DateTime From(this TimeSpan span, DateTime dt) {return dt + span;

Man, there’s LINQ alreadyCan’t we use that?

string s1 = GetS1();

string s2 = GetS2();

string res =

string.Empty;

if(s1 != null && s2 != null){

res = s1 + s2;

var res =

from a in GetS1()

from b in GetS2()

select a + b;

public class Maybe<T> {

public T Value { get; private set; }public bool HasValue { get; private set; }

private Maybe() { HasValue = false; }

public Maybe(T value) {Value = value;HasValue = true;

public static readonly Maybe<T> Nothing = new Maybe<T>();}

public static Maybe<T> ToMaybe<T>(this T value) {return new Maybe<T>(value);

public static Maybe<U> SelectMany<T, U>(this Maybe<T> src, Func<T, Maybe<U>> f) {

if (!src.HasValue) {return Maybe<U>.Nothing;

}return f(src.Value);

Important

• LINQ is a Monad

• F# Workflows are monads

• What isn’t?!

"[W]hen the designers of F# talked with the designers of Haskell about this, they agreed that the word monad is a bit obscure and sounds a littledaunting and that using other names might be wise.“

[F# Workflows and Haskell Monads, Expert F#, p232]

C# is no fun.

Want more!

Yeah?! F# you!

Workflows

type Чо<'a> =| Ничо| Чото of 'a

let bindMaybe x f = match x with| Ничо -> Ничо| Чото y -> f y

type MaybeBuilder() =member x.Return(what) = Чото whatmember x.Bind(m, f) = bindMaybe m f

let чокак = new MaybeBuilder()

Workflows

let first = чокак ,

let! x = Чото 6let! y = Чото 5return (x + y)

let second =чокак ,

let! x = Ничоlet! y = Чото 5return x+y

Syntactic sugar

Sweeties

• Partial application

• Pipelining

• Composition

• List comprehension

• Operators overriding

• AST modifications

• Measurement units

Million years ago there wasn’t LINQAnd I still program C# 2. Can I have some DSL?

AdHoc LINQ

Calculation<Item> calculation =

Time.Between(

Select.First(thisYear),

Select.Last(thisYear)

SAMPLES

Simples DSLs on .NET

Validation DSL : IronPython

discussion demo discussion

public class User : ValidationBase

[Validation("first_name_length")]

public string FirstName { get; set; }

<![CDATA[result = property_value != None and len(property_value) >= 2]]>

</rule>

PythonEngine::Execute(“python code here”)

Validation DSL : Boo

ASP.NET MVC

Application

Model (C#)

Rules (Boo)

public class User

public string Username { get; set; }

public string Password { get; set; }

rule_for "User":

validate def(x):

results = create_results()

if string.IsNullOrEmpty(x.Username)

return results

Boo.Lang.Interpreter. InteractiveInterpreter_interpreter;

Func<List<ValidationResult>> createResults = (() => new List<ValidationResult>());

_interpreter.SetValue("create_results", createResults);

results.Add(fail("Username and Password are required"))

CompilerContext ctx = _interpreter.EvalCompilerInput(newFileInput(_filePath));

foreach (CompilerError error in ctx.Errors)

sb.AppendLine(error.Message);}

Object2RSS DSL : Boo

ASP.NET MVC

Application

Model (C#)

Rules (Boo)

public class Product{

public int Id { get; set; }

public string Name { get; set; }

public string Description { get; set; }

public double Price { get; set; }

public DateTime CreateDate { get; set; }

public Manufacturer Manufacturer { get; set; }}

rule_for "Product":

title def(x):

return "${x.Manufacturer.Name.ToUpper()} -${x.Name}"

description def(x):

return x.Description

link def(x):

return "http://codevoyeur.com/products/${x.Id}"

pubDate def(x):

return x.CreateDate.ToString("s")

var engine = new RssDslEngine();foreach (T item in items)

{writer.WriteStartElement("item");List<string> fields = RssFieldFactory.Create();fields.ForEach(x =>

writer.WriteElementString(x, engine.Execute(item, x)));writer.WriteEndElement();

public string Execute(object o, string field){

string ruleName = o.GetType().Name;if (_rules.ContainsKey(ruleName)){

return _rules[ruleName][field].Invoke(o);}else{

throw new ApplicationException("Invalid rule name");

SPECTER FRAMEWORK

A BDD framework for .NET and Mono

MiniBar specification tutorial

import Specter.Frameworkimport Bender context "At Bender's bar":

_bar as duck setup:

subject _bar = Bender.MiniBar() specify { _bar.DrinkOneBeer() }.Must.Not.Throw() specify "If I drink 5 beers then I owe 5 bucks":

for i in range(5): _bar.DrinkOneBeer()

_bar.Balance.Must.Equal(-5) specify "If I drink more than ten beers then I get drunk":

{ _bar.DrinkOneBeer() }.Must.Throw()

_bar as duck setup:

[NUnit.Framework.TestFixture]class EmptyStack:

_bar as duck setup:

[NUnit.Framework.SetUp] def SetUp():

subject _bar = Bender.MiniBar()

_bar as duck setup:

[NUnit.Framework.Test]def BarDrinkOneBeerMustNotThrow():

Assert.DoesNotThrow(_bar. DrinkOneBeer())

_bar as duck setup:

[NUnit.Framework.Test]def IfIDrink5BeersThenIOwe5Bucks():

for i in range(5):_bar.DrinkOneBeer()

Int32MustModule.Must(_bar.Balance, “Bar balance must equal -5").Equal(-5)

_bar as duck setup:

[NUnit.Framework.Test]def IfiDrinkMoreThanTenBeersThenIGetDrunk():

Assert.Throws((typeof(InvalidOperationException), _bar.DrinkOneBeer())

namespace Bender

class MiniBar:

def DrinkOneBeer():

[getter(“Balance”)+

_balance = 0

namespace Bender

class MiniBar:

def DrinkOneBeer():

_balance--

if _balance < -10:

raise System.Exception("i'mdrunk")

[getter(“Balance”)+

_balance = 0

Need more?

• http://www.microsoft.com/soa/products/oslo.aspx

• http://www.jetbrains.com/mps/index.html

• http://blogs.msdn.com/wesdyer/archive/2008/01/11/the-marvels-of-monads.aspx

• http://www.google.com/

Resources

• http://www.code-magazine.com/article.aspx?quickid=0902041&page=1 (Building Domain Specific Languages in C#)

• http://bradfordcross.blogspot.com/2009/01/external-dsl-vs-internal-dsl-smack-down_24.html (External DSL vs. Internal DSL Smack Down)

Resources

• http://www.paulgraham.com/

• http://martinfowler.com/

• http://en.wikipedia.org/wiki/Domain-specific_programming_language

• http://msdn.microsoft.com/en-us/library/bb126235.aspx

Building DSLs On CLR and DLR (Microsoft.NET)

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