F# Type Providers in Depth

F# Type Providers in Depth

• 1.
  F# Type Providersin Depth Tomas Petricek @tomaspetricek | http://tomasp.net
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  F# 3.0 inVisual Studio 11
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  The Problem Meta-data <s:complexType name="Session"> <s:sequence> <s:element minOccurs="0" maxOccurs="1" information name="CustomerID" type="s:string" /> <s:element minOccurs="0" maxOccurs="1" name="CustomerName" type="s:string" /> ≠ <s:element minOccurs="0" maxOccurs="1" name="BranchNumber" type="s:string" /> <s:element minOccurs="0" maxOccurs="1" F# type name="SessionKey" type="s:string" /> <s:element minOccurs="0" maxOccurs="1" name="ChosenDeliverySlotInfo" declaration type="s:string" /> <s:element minOccurs="0" maxOccurs="1" name="CustomerMessageOfTheDay" type="s:string" /> type Session = <s:element minOccurs="0" maxOccurs="1" name="CustomerForename" { CustomerID : int type="s:string" /> CustomerName : string </s:sequence> </s:complexType> BranchNumber : int SessionKey : string ChosenDeliverySlotInfo : string CustomerMessageOfTheDay : string CustomerForName : string }
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  The Problem
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  Levels of DataAccess Expression Scale Program Scale Dynamic typing Code generation Internet Scale Type providers
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  Type providers change how you think about programming!
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  DEMO: WORLD BANK
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  What is aType Provider?
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  How are TypeProviders used? Type provider IDE Compiler IntelliSense for Type-Check Compile using Generated Types Imported Types Type Provider
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  Type Providers for.NET Hiding code generation Web Services (WSDL) SQL databases (LINQ to Entities) Erasing provided types REST services (World Bank) Schematized web (Freebase)
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  DEMO: WSDL, SQL,ODATA
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  Queries in F# Canbe turned to quotations query { for movie in netflix.Titles do where (movie.Name.Contains(search)) select movie } Extensible query language query { for index in Numbers do reverse takeWhile index > 10 }
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  Implementing Type Providers public interface ITypeProvider { Type[] GetTypes(); Expression GetInvokerExpression ( MethodBase method, ParameterExpression[] params ); event EventHandler Invalidate; }
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  Design Considerations Choosing theright view Provide the right projection Inferring structure from data Schema structure Refreshing the schema Caching of online schema
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  DEMO: XML TYPEPROVIDER
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  Summary The ease ofdynamic languages Generate types from schema No actual types are needed With the static typing benefits Checked at compile-time Full IntelliSense support
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  Compile-Time vs. Run-time TypeProvider Runtime API Provider Accesses Data Generates source Uses Accesses Provided code Executable
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  Compile-Time vs. Run-time TypeProvider Runtime API Provider Accesses Data Generates source Provided code Executable
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  Structure of aSimple Provider [<TypeProvider>] type SampleTypeProvider(config: TypeProviderConfig) = inherit TypeProviderForNamespaces() // Define new type Samples.GeneratedType let thisAssembly = Assembly.GetExecutingAssembly() let providedType = ProvidedTypeDefinition( ... ) do // Add property 'Hello' that just returns a string ProvidedProperty ( "Hello", typeof<string>, IsStatic = true, GetterCode = fun args -> <@@ Runtime.lookup "Hello" @@>) |> providedType.AddMember // Register the type with the compiler this.AddNamespace(namespaceName, [ providedType ])