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Neat Sample: F# and Freebase

  • Article

Jomo Fisher – The web service at Freebase.com lets you access all sorts of structured data from a web service. Here’s a sample that shows you how to access this data from F#. It uses DataContract and the JSON serializer. The code below reads and prints the elements of the periodic table.

Code Snippet

  1. // Freebase.fsx

  2. // Example of reading from freebase.com in F# using DataContract and JSON serializer

  3. // by Jomo Fisher

  4. #r "System.Runtime.Serialization"

  5. #r "System.ServiceModel.Web"

  6. #r "System.Web"

  7. #r "System.Xml"

  9. open System

  10. open System.IO

  11. open System.Net

  12. open System.Text

  13. open System.Web

  14. open System.Security.Authentication

  15. open System.Runtime.Serialization

  17. [<DataContract>]

  18. type Result<'TResult> = {

  19.     [<field: DataMember(Name="code") >]

  20.     Code:string

  21.     [<field: DataMember(Name="result") >]

  22.     Result:'TResult

  23.     [<field: DataMember(Name="message") >]

  24.     Message:string

  25.     }

  27. [<DataContract>]

  28. type ChemicalElement = {

  29.     [<field: DataMember(Name="name") >]

  30.     Name:string

  31.     [<field: DataMember(Name="boiling_point") >]

  32.     BoilingPoint:string

  33.     [<field: DataMember(Name="atomic_mass") >]

  34.     AtomicMass:string

  35.     }

  37. let Query<'T>(query:string) : 'T =

  38.     let query = query.Replace("'","\"")

  39.     let queryUrl = sprintf "https://api.freebase.com/api/service/mqlread?query=%s" "{\"query\":"+query+"}"

  41.     let request : HttpWebRequest = downcast WebRequest.Create(queryUrl)

  42.     request.Method <- "GET"

  43.     request.ContentType <- "application/x-www-form-urlencoded"

  45.     let response = request.GetResponse()

  47.     let result =

  48.         try

  49.             use reader = new StreamReader(response.GetResponseStream())

  50.             reader.ReadToEnd();

  51.         finally

  52.             response.Close()

  54.     let data = Encoding.Unicode.GetBytes(result);

  55.     let stream = new MemoryStream()

  56.     stream.Write(data, 0, data.Length);

  57.     stream.Position <- 0L

  58.     

  59.     let ser = Json.DataContractJsonSerializer(typeof<Result<'T>>)

  60.     let result = ser.ReadObject(stream) :?> Result<'T>

  61.     if result.Code<>"/api/status/ok" then

  62.         raise (InvalidOperationException(result.Message))

  63.     else

  64.         result.Result

  66. let elements = Query<ChemicalElement array>("[{'type':'/chemistry/chemical_element','name':null,'boiling_point':null,'atomic_mass':null}]")

  68. elements |> Array.iter(fun element->printfn "%A" element)

Let me know if there are other F# samples you’d like to see.

This posting is provided "AS IS" with no warranties, and confers no rights.