string representation of F# function signature

Question

When I\'m working in the F# REPL fsharpi whenever I enter a new function the signature is printed after I\'ve entered them:

> let foo x = x;;         


        

Answer 1

You can analyze types representing F# functions, with the help of the Microsoft.FSharp.Reflection namespace. There is the caveat that generic function arguments default to System.Object, and that other F# types which may form incomplete patterns (e.g. union cases, records) are not included.

open Microsoft.FSharp.Reflection
let funString o =
    let rec loop nested t =
        if FSharpType.IsTuple t then
            FSharpType.GetTupleElements t
            |> Array.map (loop true)
            |> String.concat " * "
        elif FSharpType.IsFunction t then
            let fs = if nested then sprintf "(%s -> %s)" else sprintf "%s -> %s"
            let domain, range = FSharpType.GetFunctionElements t
            fs (loop true domain) (loop false range)
        else
            t.FullName
    loop false (o.GetType())

let foo x = x
funString foo
// val it : string = "System.Object -> System.Object"