Question

I have F# class library assembly that contains two functions:

let add a b = a + b

and

let rec aggregateList list init (op:int -> int -> int) =
    match list with
    |[] -> init
    |head::tail ->
        let rest = aggregateList tail init op
        op rest head

I have a C# console application which references the F# library and is attempting to do the following:

FSharpList<int> l = new FSharpList<int>(1, new FSharpList<int>(2, FSharpList<int>.Empty));
int result = myFsLibrary.aggregateList(l, 0, myFsLibrary.add);

However, the compiler complains that [myFsLibrary.add] cannot be converted from ‘method group’ to FSharpFunc<int, FSharpFunc<int, int>>

Answer 1

You can explicitly create a function using the FSharpFunc delegate. In C#, it is more convenient to create function that takes all arguments as a tuple, so you can do that and then convert the function to a curried type using FuncConvert. Something like:

FuncConvert.FuncFromTupled(new FSharpFunc<Tuple<int, int>, int>(args => 
    arags.Item1 + args.Item2))

However, if you need to call some F# function from your C# code, it is recommended to expose a function with a C#-friendly interface. In this case, I you can use Func delegate and the first argument should be IEnumerable instead of F#-specific list type:

module List = 
    let AggregateListFriendly inp init (op:Func<int, int, int>) =
        aggregateList (List.ofSeq inp) init (fun a b -> op.Invoke(a, b))

Then your C# appplication can just use:

List.AggregateListFriendly(Enumerable.Range(0, 10), 0, (a, b) => a + b));