Call F# code from C#

Question

I am playing around with F# and C#, and would like to call F# code from C#.

I managed to get it to work the other way around in Visual Studio by having two projects in the same solution, and adding a reference of the C# code to the F# project. After doing this, I could call C# code and even step through it while debugging.

What I am trying to do is F# code FROM C# instead of C# code from F#. I added a reference to the F# project to the C# project, but it isn't working the way it did before. I would like to know if this is possible without doing it manually.

Answer 1

Below is a working example of calling F# from C#.

As you encountered, I was not able to add a reference by selecting from the "Add Reference ... Projects" tab. Instead I did have to do it manually, by browsing to the F# assembly in the "Add Reference ... Browse" tab.

------ F# MODULE -----

// First implement a foldl function, with the signature (a->b->a) -> a -> [b] -> a // Now use your foldl function to implement a map function, with the signature (a->b) -> [a] -> [b] // Finally use your map function to convert an array of strings to upper case // // Test cases are in TestFoldMapUCase.cs // // Note: F# provides standard implementations of the fold and map operations, but the  // exercise here is to build them up from primitive elements...  module FoldMapUCase.Zumbro #light   let AlwaysTwo =    2  let rec foldl fn seed vals =     match vals with    | head :: tail -> foldl fn (fn seed head) tail    | _ -> seed   let map fn vals =    let gn lst x =       fn( x ) :: lst    List.rev (foldl gn [] vals)   let ucase vals =    map String.uppercase vals 

----- C# UNIT TESTS FOR THE MODULE -----

// Test cases for FoldMapUCase.fs // // For this example, I have written my NUnit test cases in C#.  This requires constructing some F# // types in order to invoke the F# functions under test.   using System; using Microsoft.FSharp.Core; using Microsoft.FSharp.Collections; using NUnit.Framework;  namespace FoldMapUCase {     [TestFixture]     public class TestFoldMapUCase     {         public TestFoldMapUCase()         {                     }          [Test]         public void CheckAlwaysTwo()         {             // simple example to show how to access F# function from C#             int n = Zumbro.AlwaysTwo;             Assert.AreEqual(2, n);         }          class Helper<T>         {             public static List<T> mkList(params T[] ar)             {                 List<T> foo = List<T>.Nil;                 for (int n = ar.Length - 1; n >= 0; n--)                     foo = List<T>.Cons(ar[n], foo);                 return foo;             }         }           [Test]         public void foldl1()         {             int seed = 64;             List<int> values = Helper<int>.mkList( 4, 2, 4 );             FastFunc<int, FastFunc<int,int>> fn =                 FuncConvert.ToFastFunc( (Converter<int,int,int>) delegate( int a, int b ) { return a/b; } );              int result = Zumbro.foldl<int, int>( fn, seed, values);             Assert.AreEqual(2, result);         }          [Test]         public void foldl0()         {             string seed = "hi mom";             List<string> values = Helper<string>.mkList();             FastFunc<string, FastFunc<string, string>> fn =                 FuncConvert.ToFastFunc((Converter<string, string, string>)delegate(string a, string b) { throw new Exception("should never be invoked"); });              string result = Zumbro.foldl<string, string>(fn, seed, values);             Assert.AreEqual(seed, result);         }          [Test]         public void map()         {             FastFunc<int, int> fn =                 FuncConvert.ToFastFunc((Converter<int, int>)delegate(int a) { return a*a; });              List<int> vals = Helper<int>.mkList(1, 2, 3);             List<int> res = Zumbro.map<int, int>(fn, vals);              Assert.AreEqual(res.Length, 3);             Assert.AreEqual(1, res.Head);             Assert.AreEqual(4, res.Tail.Head);             Assert.AreEqual(9, res.Tail.Tail.Head);         }          [Test]         public void ucase()         {             List<string> vals = Helper<string>.mkList("arnold", "BOB", "crAIg");             List<string> exp = Helper<string>.mkList( "ARNOLD", "BOB", "CRAIG" );             List<string> res = Zumbro.ucase(vals);             Assert.AreEqual(exp.Length, res.Length);             Assert.AreEqual(exp.Head, res.Head);             Assert.AreEqual(exp.Tail.Head, res.Tail.Head);             Assert.AreEqual(exp.Tail.Tail.Head, res.Tail.Tail.Head);         }      } } 

Answer 2

It should 'just work', though you might have to build the F# project before a project-to-project reference from C# works (I forget).

A common source of issues is namespaces/modules. If your F# code does not start with a namespace declaration, it gets put in a module with the same name as the filename, so that e.g. from C# your type might appear as "Program.Foo" rather than just "Foo" (if Foo is an F# type defined in Program.fs).