.net - How can evaluate an expression stored as a string in F#

Question

I want to do something sort of like this:

let x = 5
let y = 10

let expr = Console.ReadLine()

expr

Where one might type "x+y" in the console to store in expr.

How does one evaluate a statement like this in F#?

Ultimately, I want a user to be able to enter expressions, or a set of rules for a system, on a webpage and have them saved in a database to be applied at appropriate times in an F# library. I just don't know how to convert the entered string in to a function value in F#.

Thanks for any help you may provide!

Adam

Answer 1

I just saw Joh use quotation evaluations on his F# for game development page

      open Microsoft.FSharp.Linq.QuotationEvaluation
      ...
      let mk_gravity scale_func (up: 'Vec): 'Vec =
      let q = <@ let (*) = %scale_func in -9.81 * up @>
      q.Eval()

Alternately, if you are after simple math evaluation, you can download Edmonodo's Expression parser and evaluator from his codeplex plage - Symbolic Differentiation in C#/F#

Good luck - Ji?í