Example of a simple TypeProvider for reading AppSettings

AppSettingsTypeProvider.fs

namespace AppSettingsTypeProvider

open System
open System.IO
open System.Reflection
open Samples.FSharpPreviewRelease2011.ProvidedTypes
open Microsoft.FSharp.Core.CompilerServices
open System.Configuration

[<TypeProvider>]
type public AppSettingsProvider(config:TypeProviderConfig) as this = 
    inherit TypeProviderForNamespaces()

    let namespaceName = "AppSettingsTypeProvider"
    let currentAssembly = Assembly.GetExecutingAssembly()
    let tySettings = ProvidedTypeDefinition(currentAssembly, namespaceName, "AppSettings", Some typeof<obj>)    

    let addSettings (configFileName:string) (tyDef:ProvidedTypeDefinition) = 
        tyDef.AddXmlDocDelayed(fun () -> sprintf "Provides a strongly typed representation of the appSettings in a provided config file.")

        let filePath = Path.Combine(config.ResolutionFolder, configFileName) 
        let fileMap = ExeConfigurationFileMap(ExeConfigFilename=filePath)
        let appSettings = ConfigurationManager.OpenMappedExeConfiguration(fileMap, ConfigurationUserLevel.None).AppSettings.Settings
        
        let tryParseWith func = func >> function
            | true, value -> Some value
            | false, _ -> None

        let (|Bool|_|) = tryParseWith Boolean.TryParse
        let (|Int|_|) = tryParseWith Int32.TryParse
        let (|Double|_|) = tryParseWith Double.TryParse

        do Seq.iter (fun (key) ->   
            let keyElement = match (appSettings.Item key).Value with
                             | Int fieldValue -> ProvidedLiteralField(key, typeof<int>, fieldValue)
                             | Bool fieldValue -> ProvidedLiteralField(key, typeof<bool>, fieldValue)
                             | Double fieldValue -> ProvidedLiteralField(key, typeof<Double>, fieldValue)
                             | fieldValue -> ProvidedLiteralField(key, typeof<string>, fieldValue.ToString())

            do keyElement.AddXmlDocDelayed(fun () -> sprintf "Returns the value from the appSetting with key %s" key)
            do tyDef.AddMember keyElement ) appSettings.AllKeys 
    
    let staticParams = [ProvidedStaticParameter("configFilePath", typeof<string>)]    

    do tySettings.DefineStaticParameters(staticParams, 
        fun typeName args ->
            match args with
            | [| :? string as configFileName |] ->             
                let ty = ProvidedTypeDefinition(assembly = currentAssembly,                         
                            namespaceName = namespaceName, typeName = typeName,                         
                            baseType = Some typeof<obj>, HideObjectMethods = true)                                            
                addSettings configFileName ty                                
                ty
            | _ -> failwith "unexpected parameter values")                   
 
    do this.AddNamespace(namespaceName, [tySettings])
                           
[<assembly:TypeProviderAssembly>] 
do()

// Example of this TypeProvider in use

r "System"

r @"bin\debug\AppSettingsTypeProvider.dll"

open System
open AppSettingsTypeProvider

type settings = AppSettings<"App.config">
printfn "Test2 String: %s" settings.test2
printfn "Test Int: %i" settings.TestInt
printfn "Test Bool: %b" settings.TestBool
printfn "Test Double: %f" settings.TestDouble

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
<appSettings>
<add key="test2" value="Some Test Value 5"/>
<add key="TestInt" value="102"/>
<add key="TestBool" value="True"/>
<add key="TestDouble" value="10.01"/>
</appSettings>
</configuration>