Using c# delegates with f# functions

Question

I am trying to call a c# function from f# where the c# function takes a function (delegate?) as a parameter and I need this argument to be a f# function. Eg:

Sample

Answer 1

If you want to create a delegate from a function in F#, you can use the new operator and give it the function as an argument:

let function_1 (x:double) (y:double) = 
    ()

Program.call_func(s, new Action<double, double>(function_1))

But, for some reason, if try to use the same approach with a delegate that contains ref, you get this error:

This function value is being used to construct a delegate type whose signature includes a byref argument. You must use an explicit lambda expression taking 2 arguments.

So, if you follow the advice given by the error message, you can write the following:

let function_1 (x:double) (y:double byref) = 
    y <- 6.0

Program.call_func(s, new fn(fun x -> fun y -> function_1 x &y))

This compiles, and works as expected.

Note that to modify the parameter y, you have to use the <- operator. Using let y = 6.0 declares completely different variable that shadows the parameter.