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

AFAIK, there's no function in FSharp.Core for getting a type's string representation as it would appear to the compiler (though maybe there's something in FSharp.Compiler.Services -- I haven't checked). Here's a small function that works for most simple uses:

open System

let (|TFunc|_|) (typ: Type) =
    if typ.IsGenericType && typ.GetGenericTypeDefinition () = typeofint>.GetGenericTypeDefinition () then
        match typ.GetGenericArguments() with
        | [|targ1; targ2|] -> Some (targ1, targ2)
        | _ -> None
    else
        None

let rec typeStr (typ: Type) =
    match typ with
    | TFunc (TFunc(_, _) as tfunc, t) -> sprintf "(%s) -> %s" (typeStr tfunc) (typeStr t)
    | TFunc (t1, t2) -> sprintf "%s -> %s" (typeStr t1) (typeStr t2)
    | typ when typ = typeof -> "int"
    | typ when typ = typeof -> "string"
    | typ when typ.IsGenericParameter -> sprintf "'%s" (string typ)
    | typ -> string typ


typeStr typeof<(string -> (string -> int) -> int) -> int>
// val it: string = "string -> (string -> int) -> int"
typeStr (typeofint>.GetGenericTypeDefinition())
// val it: string = "'T -> 'TResult"

You can easily write a function on top of this to use typeStr on a value's type:

let valTypeString x = typStr (x.GetType ())