Why am I getting F# error FS0039: The namespace or module 'Http' is not defined

Question

In Visual Studio 2015 and 2017, I'm trying out the Http class from several F# examples in FSharp Interactive, and I keep getting:

error FS0039: The namespace or module 'Http' is not defined

Here's the sample:

open FSharp.Data
let response = Http.RequestString("http://api.themoviedb.org/3/search/movie", silentHttpErrors = true)

This is clearly due to the version of FSharp.Data. Is there a way to specify the correct version for FSharp Interactive? What version of FSharp.Data contains the Http module?

Answer 1

Based on the comments, I put together a script to install Paket, intitialise it and then optionally install the dependencies whenever the script was run.

/// install.paket.fsx
open System
open System.IO

printfn "Initialising..."
Environment.CurrentDirectory <- __SOURCE_DIRECTORY__
// invisibly run a command (paket.exe in this case)
let init paket =
    let psi = new System.Diagnostics.ProcessStartInfo(paket)
    psi.Arguments <- "init"
    psi.UseShellExecute <- false
    let p = System.Diagnostics.Process.Start(psi)
    p.WaitForExit()
    p.ExitCode

if not (File.Exists "paket.exe") then
    printfn "installing paket"
    let url = "http://fsprojects.github.io/Paket/stable"
    use wc = new Net.WebClient()
    let tmp = Path.GetTempFileName()
    let stable = wc.DownloadString(url)
    wc.DownloadFile(stable, tmp)
    File.Move(tmp,Path.GetFileName stable)
    printfn "paket installed"
    System.Threading.Thread.Sleep(100)
    printfn "initialising paket"
    init "paket.exe" |> ignore
    System.Threading.Thread.Sleep(200)
    printfn "paket initialised"
else
    printfn "paket already exists"

/// install.dependencies.fsx

open System.IO
printfn "Installing dependencies"
System.Environment.CurrentDirectory <- __SOURCE_DIRECTORY__
#r "paket.exe"

open Paket
let dependencies = Paket.Dependencies.Locate(__SOURCE_DIRECTORY__)

printfn "%s" dependencies.DependenciesFile

if not (File.Exists "packages/Newtonsoft.Json/lib/net40/Newtonsoft.Json.dll") then
    printfn "installing nuget depenencies"
    // either use the dependencies.Install to add dependencies in the paket.dependencies file
    //dependencies.Install true |> ignore
    // or install them by name
    // I remove the existing versions
    dependencies.Remove "FSharp.Data"
    dependencies.Remove "Newtonsoft.Json 8.0.3"
    // then add them (because I'm pedantic about the way the dependencies file looks)
    dependencies.Add "FSharp.Data"
    dependencies.Add "Newtonsoft.Json 8.0.3"
    printfn "nuget depenencies installed"
else
    printfn "nuget depenencies already exist"

printfn "Dependencies installed"

Note the use of 8.0.3 for Newtonsoft.Json, The latest version brings over 20 additional dependencies, so I've found a nice old version that's very self contained. You may leave the version number out if you want the latest.

Then, I use these scripts in a shared utilities.fsx for reusable functionality

System.Environment.CurrentDirectory <- __SOURCE_DIRECTORY__
#load "install.paket.fsx"
#load "install.dependencies.fsx"

#r "packages/fsharp.data/lib/net40/fsharp.data.dll"
#r "packages/Newtonsoft.Json/lib/net40/Newtonsoft.Json.dll"

open FSharp.Data
open FSharp.Data.HtmlAttribute
open FSharp.Data.HtmlNode
open FSharp.Data.HttpRequestHeaders
open Newtonsoft.Json
open System.Net
open System.IO
// utilities like authentication, Http requests and JSON (de)serialization

Finally, I reference the whole lot in my target script by just loading utilities:

System.Environment.CurrentDirectory <- __SOURCE_DIRECTORY__
#load "utilities.fsx"
open Utilities

which takes care of all the dependencies. These can be run from Visual studio with the Alt + Enter key combination or from the command line with fsi.exe MyScript.fsx