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Internal Domain-specific Languages in C#

Internal Domain-specific Languages in C#. By Chad Myers LosTechies.com. Introduction. Housekeeping Stuff Meet the Presenter ALT.NET LosTechies.com. Quick Primer on Advanced C# 3.0. Lambda Functions Inline and Multiline Block Closures Type, List, and Dictionary Initializers

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Internal Domain-specific Languages in C#

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  1. Internal Domain-specific Languages in C# By Chad MyersLosTechies.com

  2. Introduction • Housekeeping Stuff • Meet the Presenter • ALT.NET • LosTechies.com

  3. Quick Primer on Advanced C# 3.0 • Lambda Functions • Inline and Multiline • Block • Closures • Type, List, and Dictionary Initializers • Type Inferrence • Basics of Expression Trees • Static Reflection

  4. Internal DSL Introduction • What? – “Language within a Language” for targeted, specific purpose • Why? –Toenhance the usability of an API designed and highly targeted for a specific purpose • Who?– Martin Fowler, Jeremy Miller, Ayende Rahien, Jay Fields • When? – In .NET, primarily since C# 3.0 (mini-DSLs in .NET have existed since 1.1) • How?– Attend this Workshop! Read Fowler, Miller, Rahien, Fields

  5. Internal DSL Concepts • Bending an existing language and compiler • Unconventional – but still disciplined – use of language techniques (Language Oriented Programming) • Focus on Flow, Comprehension and Accelerated Use of Finished Product • Should Be (Outwardly…): • Expressive • Efficient/Productive • Conventional (in the context of the domain) • Discoverable, Flowing

  6. Internal DSL Strategies • Small DSLs • Problem/Purpose Identification • Pattern Application • Refactoring • Large DSLs • Problem/Purpose Identification • Major component Identification and Minimal Design • Pattern Application • Refactoring

  7. Internal DSL Form and Type • End Result • Generative • Non-Generative • Internal Structure • Semantic Model (Internal & External) • No Model

  8. Questions Here • Before we get into the meat, any questions?

  9. Internal DSL Patterns • Building Block Concepts • Context Variables and State Management • Generic Type Specifiers • Building Block Patterns • Method Chaining • Nested Function • Nested Closure • Literal Type/Collection Expression (Initializers) • Dynamic Reception (Extension Methods) • Parse Tree Manipulation (Expression Trees)

  10. Internal DSL Patterns • Structural Patterns • Expression Builder • Object Scoping • Delegation (Nested Closures Revisited) • Convention

  11. Method Chaining Pattern • Start with Host Object • Return Host Object from Each Call • Modifies State or Performs an Action • Purpose: • Assembly/Population of an Object or Objects • Allows for in-line or multi-line statements • Provides clear path for consumers • Examples: • System.DateTime • System.String

  12. Nested Function Pattern • Small, Focused, Deterministic • Encapsulates Frequent Tasks • Helps Keep Flow • Helps Enhance Language • Examples: • DateTime.Parse(), *.Parse() • TimeSpan.FromMinutes

  13. Nested Closure Pattern • Delegation • Scoping • Physical Separation of Tasks • Deterministic Resolution of Task • Solves “Rathole” Problem • Examples: • Registry.Scan (StructureMap) • PersistenceModel.ForEach (Fluent Nhibernate)

  14. Literal Type Expression Pattern • Type/Collection/Dictionary Initializers • Can Replace Method Chaining in Many Circumstances • Can be More Expressive, in Less Spaces • Examples: • MsSqlConifgurationTester (Fluent Nhibernate)

  15. Dynamic Reception Pattern • In C# 3.0, this means Extension Methods • In C# 4.0, much, much more • Attaching Different Behavior to Existing API • Extensibility Point for Existing DSLs • Allows for Different Grammars for Same API • Examples: • XmlExtensions (Fluent Nhibernate) • Specification Extensions (Fluent Nhibernate)

  16. Parse Tree Manipulation Pattern • In C#, this means Expression Trees • Useful for Static Reflection • Can Compose Expressions • Examples: • ClassMap<T> (Fluent Nhibernate) • EntityQuery stuff (Fluent Nhibernate)

  17. Questions • Any questions on building block patterns?

  18. Expression Builder Pattern • State Management • Progressive Interfaces • The “Rathole” Problem • Examples: • CascadeExpression (Fluent Nhibernate) • ManyToManyPart (Fluent Nhibernate) • ActionLinkExpression (Dovetail) • ExpressionBase (Dovetail)

  19. Object Scoping Pattern • Can be used directly, or serves as base class • Contains starter methods • Launching point for other patterns • Examples: • Registry (StructureMap) • PersistenceModel (Fluent Nhibernate)

  20. Delegation (Nested Closures) • Can also be structural • Examples: • ObjectFactory.Initialize (StructureMap)

  21. Conventions • Discovery of types • Identification of interesting types • Application • Examples: • ITypeScanner (StructureMap) • AutoPersistenceModel (Fluent Nhibernate)

  22. Questions • Any questions on structural patterns?

  23. In Practice: Fairy Tale Builder • Build a model-based generative Internal DSL for writing a fairy tale story • End result: Print the story to the debug window • Demonstrate as many patterns as possible in one DSL

  24. Fairy Tale Model • FairyTale object • Story Parts (Intro, focus, plot, ending) • Rendering

  25. Fairy Tale Builder • Delegation -- Nested Closure • Expression Builder in closure • Method Chaining with Generic Type Specifiers • Literal Type Expressions • Parse Tree Manipulation • Dynamic Reception

  26. Questions • Any questions on Fairy Tale Builder?

  27. Closing • Chad Myerschad@chadmyers.comhttp://chadmyers.lostechies.com • Martin Fowler’s DSL WIPhttp://martinfowler.com/dslwip

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