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F# Intro for Scala Developers
- 1. Boston Area Scala Enthusiasts, April 11 th , 2011 • Microsoft NERD • Cambridge, MA let talk = things |> Seq.filter (fsharp >> cool) |> Seq.map scala |> Seq.take n
- 16. C# 3.0 – can do this Func<Func<int,string,bool>, Func<int,string,Tuple<int,string>>,int,string, Tuple<int,string>> filtermap = (f, m, a, b) => { if (f(a,b)) { return m(a,b); } else { return Tuple.Create(a, b); } }; Func<int,string,bool> filter = ...; Func<int,string,Tuple<int,string>> map = ...; var t = filtermap(filter, map, 1, "Hello"); var tInt = t.Item1; var tString = t.Item2;
- 18. C# 3.0/4.0 – a lot better than Java, but still not a full functional language “ Mads Torgersen, C# Product Manager http://blogs.msdn.com/b/madst/archive/2007/01/23/is-c-becoming-a-functional-language.aspx People who are functional programmers by night and have to write C# by day will find that the daily headache sets in a little later in the afternoon.
- 43. let arr = [| 1; 2; 3; 4; 5 |] let list = [ for i in 0 .. 2 .. 24 -> i * 4 ] type Country = { Name : string; Cities: string seq } let countries = [ { Name = "Spain"; Cities = ["Barcelona"; "Madrid" ] } { Name = "Germany"; Cities = ["Berlin"; "Frankfurt" ] } { Name = "USA"; Cities = ["Boston"; "New York ] } { Name = "India"; Cities = ["Bhopal"; "Mumbai" ] } ] let populations : IDictionary<string,long> = ... let mySeq = seq { for c in countries do for city in c.Cities do if city.StartsWith("b") then let pop = populations.["city"] yield city, country, pop }
- 44. mySeq |> Seq.filter (fun (_,_,pop) -> pop > 1000000) |> Seq.sortBy (fun (_,_,pop) -> -pop) // descending |> Seq.map (fun (city,c,pop) -> sprintf "%s, %s. Pop.: %d" city c pop)
- 49. let mapReduce() = [ 1; 2; 3; 4; 5 ] |> List.map (( * ) 2) |> List.reduce (fun acc elem -> acc + elem) let res = mapReduce() val it : int = 30 let words = [ "one"; "two"; "three"; "four"; "five" ] let flatMapDistinctToUpperSorted() = let chars = words |> List.map (fun w -> w.ToCharArray() |> List.ofArray) |> Seq.ofList // Seq needed for certain functions |> Seq.concat // flatten |> Seq.distinct |> Seq.map (fun c -> System.Char.ToUpper(c)) |> Seq.sort chars let res2 = flatMapDistinctToUpperSorted() val it : seq<char> = seq ['E'; 'F'; 'H'; 'I'; ...]
- 61. /// Our asynchronous agent processor - skeleton let agent = MailboxProcessor.Start(fun inbox -> let rec loop ticket = async { let! msg = inbox.Receive() match msg with | Echo(echo, channel) -> // ... return! loop (ticket + 1L) | AuditReportRequest(channel) -> // ... | NumMessages(channel) -> // ... | Deposit(name,amt,channel) -> // ... return! loop (ticket + 1L) | Withdrawal(name,withdrawer,amt,channel) -> // ... return! loop (ticket + 1L) | Stop -> () // stop looping } loop EmptyTicket)
- 62. /// Our asynchronous agent processor let agent = MailboxProcessor.Start(fun inbox -> let rec loop ticket = async { let! msg = inbox.Receive() match msg with | Echo(echo, channel) -> channel.Reply("ECHO: " + echo) return! loop (ticket + 1L) | AuditReportRequest(channel) -> channel.Reply(createReport()) return! loop (ticket + 1L) | NumMessages(channel) -> channel.Reply(n) return! loop (ticket + 1L)
- 63. /// Our asynchronous agent processor let agent = MailboxProcessor.Start(fun inbox -> let rec loop ticket = async { let! msg = inbox.Receive() match msg with // ... | Deposit(name,amt,channel) -> let t = ticket if accountMap.ContainsKey(name) then let a = accountMap.[name] a.Deposit(amt) |> ignore let msg = addMsg (t, name, "Deposit", amt, Success) channel.Reply(msg) else let msg = addMsg (t, name, "Deposit", amt, Failure("Account " + name + " not found")) channel.Reply(msg) return! loop (ticket + 1L)
- 64. // Scala style syntax helper - almost let (<!) (a : AccountAgent) (req : MessageRequest) = a.SendMessage req let agent = new AccountAgent(bankAccounts) let s = agent.Echo("Hello world!") let mutable n = agent.MessageCount() printfn "Messages: %d" n printfn "Making deposits..." agent <! DepositRequest("Alice", 1200M) |> ignore agent <! DepositRequest("Bob", 200M) |> ignore agent <! DepositRequest("Carol", 300M) |> ignore agent <! DepositRequest("Dave", 400M) |> ignore n <- agent <! MessageCountRequest |> getReply |> int64 printfn "Messages: %d" n
- 68. // Simple Active Pattern – returns a boolean let (|UpperChar|) c = Char.ToUpper(c) // Partial Active Pattern – Some (with possible transformation) // or None let (|IsDigit|_|) c = if Char.IsDigit(c) then Some(int c) // convert char to an int else None // Active Pattern with parameters + reusing above APs let (|IsDigitInRange|_|) rangeStart rangeEnd c = match c with | IsDigit(n) -> if n >= rangeStart && n <= rangeEnd then Some(n) else None | _ -> None
- 69. // Partial Active Pattern let (|Match|_|) (regex : Regex) input = if regex.IsMatch(input) then Some(regex.Match(input)) else None // Active pattern - // "partitions" input into one of several "classes" let (|Zip|Country|State|City|Invalid|) s = match s with | Match regexZip m -> Zip(m |> result "zip", "", "", "") | Match regexCity m -> City("",resCountry m,resState m,m |> result "city") | Match regexState m -> State("", resCountry m, resState m, "") | Match regexCountry m -> Country("", resCountry m, "", "") | _ -> Invalid
- 70. // Using Active Pattern, this is simplified let parse input = match input with | Zip(z, _, _, _) -> { Country = ""; State = ""; City = ""; Zip = z } | Country(_, c, _, _) -> { Country = c; State = ""; City = ""; Zip = "" } | State(_, c, s, _) -> { Country = c; State = s; City = ""; Zip = "" } | City(_, co, st, ci) -> { Country = co; State = st; City = ci; Zip = "" } | Invalid -> { Country = ""; State = ""; City = ""; Zip = "" }
- 71. // Partial Active Pattern - returns Option. If Some(_) then returns a LocationInfo let (|ValidLocation|_|) input = match input with | Zip(z, _, _, _) -> Some({ Country = ""; State = ""; City = ""; Zip = z }) | City(_, co, st, ci) -> Some({ Country = co; State = st; City = ci; Zip = "" }) | _ -> None // Is this a "valid" location? // Use of "function" let parseIsValid = function | ValidLocation(loc) -> true | _ -> false // Same as... let parseIsValid2 input = match input with | ValidLocation(loc) -> true | _ -> false
- 72. // Partial/Parameterized Active Pattern // Does this have a zip code contained in zipList? let (|HasZip|_|) (zipList : string list) input = match input with | Zip(z, _, _, _) when (zipList |> List.exists (fun x -> x = z)) -> Some(z) //| City(_, co, st, ci) -> None // could do a lookup here... | _ -> None let isBoston input = // 02101 - 02299 let bostonZips = [ for i in 2101 .. 2299 -> sprintf "0%d" i ] match input with | HasZip bostonZips z -> true | _ -> false
- 86. let runTest gen = let parser = new FormatParser(gen) let workflow = parse { let! dateT = parser.Parse dt let! _ = parser.Parse x1 // we don't care about X() let! tempT = parser.Parse t let! _ = parser.Parse x2 let! pressureT = parser.Parse p let! _ = parser.Parse x3 let! relhumT = parser.Parse rh let date, temperature, pressure, relhum = dateT |> gs, tempT |> gf, pressureT |> gf, relhumT |> gf let tp = temperature * pressure return (date, temperature, pressure, relhum, tp) } let result = ParseRunner.Run workflow match result with | ParseSuccess(d,t,p,r,tp) -> printfn "Success: Weather on %s: Temp: %f, Pres: %f, RH: %f" d t p r | ParseFailure(msg, pos) -> printfn "Failure: %s at line %d, pos %d" msg pos.Line pos.Column let runSuccess() = runTest gen1 let runFailure() = runTest gen2