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;;
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"
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 () = typeof<int->int>.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> -> "int"
| typ when typ = typeof<string> -> "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 (typeof<int->int>.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 ())