FSharp embedded API add variables

Question

Using the Fsharp.Compiler.Serice Interactive API I'd like to set variables to my FsiEvaluationSession object. Is this possible? Or is there another way to embed f# into an application for embedded-scripting purposes?

Answer 1

I don't think there is a direct way to do this, but there is a lovely workaround:

// Define a mutable variable with default value
fsiSession.EvalInteraction "let mutable myVar = Unchecked.defaultof<int>"

// Create a function that sets the value of the variable
let f = evalExpressionTyped<int -> unit> "fun x -> myVar <- x"  

// Run the function to set the value of `myVar` to whatever we want
f 42

// As a bonus, use variable shadowing to make it immutable
fsiSession.EvalInteraction "let myVar = myVar"

This uses the evalExpressionTyped helper from the FCS documentation.