http://stackoverflow.com/questions/21747666/deserializing-f-map-by-json-net

gistfile1.fs

// Install http://www.nuget.org/packages/Fleece

open Fleece
open FSharpPlus

let json = """{
  "1": "one",
  "2": "two",
  "3": "three"
}"""

let intMap = 
    monad {
        let! stringMap = parseJSON json : Map<string, string> ParseResult
        let! kvParsed = stringMap |> traverse (fun (KeyValue(k,v)) -> 
                                                match tryParse k : int option with
                                                | Some i -> Success (i,v)
                                                | _ -> Failure ("Invalid integer " + k))
        return Map.ofSeq kvParsed
    }

// intMap is of type Choice<Map<int, string>, string>

printfn "%A" intMap