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F#
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What is it?
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It is a strongly typed,
functional first
language
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multiparadigm
functional, imperative and object oriented
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originally developed by
Microsoft Research
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now controlled by
F# Foundation
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Apache 2 Licensed
Runs on: CLR (Mono/.Net)
Compiles to JavaScript
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originated from ML
inspired by C#, OCAML, Haskell, …
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Language
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let x = 5
let y = 10
let z = x + y
z = 10
Basic Syntax (Values)
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let addStr x y = (x + y).ToString()
val addStr : x:int -> y:int -> string
Basic Syntax (Arrow notation)
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Type inference
Happens everywhere
Parameters, Values, Generics
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let add (x : int) (y : int) = x + y
Type inference
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let add (x : int) (y : int) = x + y
let add x y = x + y
Type inference
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let add (x : int) (y : int) = x + y
let add x y = x + y
add 5 10
Type inference
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let add (x : int) (y : int) = x + y
let add x y = x + y
add 5 10
add 3.14 4.56
Type inference
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let add (x : int) (y : int) = x + y
let add x y = x + y
add 5 10
add 3.14 4.56
add 3.14 10
Type inference
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let sign num =
if num > 0 then "positive"
elif num < 0 then "negative"
else "zero"
Type inference (more)
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let sign num =
if num > 0 then "positive"
elif num < 0 then "negative"
else 0
Type inference (more)
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type IAnimal = interface…
Type inference (more)
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type IAnimal = interface…
type Dog = class interface IAnimal…
Type inference (more)
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type IAnimal = interface…
type Dog = class interface IAnimal…
let getName (l : IAnimal) = …
Type inference (more)
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type IAnimal = interface…
type Dog = class interface IAnimal…
let getName (l : IAnimal) = …
let doStuffWithDog (d : Dog) = …
Type inference (more)
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type IAnimal = interface…
type Dog = class interface IAnimal…
let getName (l : IAnimal) = …
let doStuffWithDog (d : Dog) = …
let takesStuff s =
doStuffWithDog(s)
getName(s)
Type inference (more)
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Type inference (Generics)
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let giveMeAThree x = 3
'a -> int
Type inference (Generics)
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let throwAwayFirstInput x y = y
'a -> 'b -> 'b
Type inference (Generics)
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Functional
Programming
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Pattern Matching
Describes control flow
patterns match sequentially
Checked for completness
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let getPrice name =
match name with
| "banana" -> 0.79
| "watermelon" -> 3.49
| "tofu" -> 1.09
| _ -> nan
Pattern Matching
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let getPrice = function
| "banana" -> 0.79
| "watermelon" -> 3.49
| "tofu" -> 1.09
| _ -> nan
Pattern Matching
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let sign = function
| 0 -> 0
| x when x < 0 -> -1
| x when x > 0 -> 1
Pattern Matching
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Recursion
Basic concept of FP
Function calling itself
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let rec fact x =
if x < 1 then 1
else x * fact (x - 1)
Recursion
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let rec count n =
if n = 1000000 then
printfn "done"
else
if n % 1000 = 0 then
printfn "n: %i" n
count (n + 1)
Recursion (Tail)
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Higher order functions
Function taking a function as
argument and/or returning a
function
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let passFive f = (f 5)
val passFive : (int -> 'a) -> 'a
Higher order functions
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let map it converter = converter it
val map : 'a -> ('a -> 'b) -> 'b
Higher order functions
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let add x y = x + y
let addFive = add 5
Higher order functions
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let add x y = x + y
val add : int -> int -> int
let addFive = add 5
val addFive : (int -> int)
Higher order functions
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Option Types
The “null” of functional
programming
Some or None
Explicitly stat that some can be
nothing
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> let div x y = x / y
val div : int -> int -> int
> div 10 5
val it : int = 2
> div 10 0
Option Types
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let sdiv x y =
match y with
| 0 -> None
| _ -> Some(x/y)
val sdiv : int -> int -> int option
Option Types
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> safediv 10 5
val it : int option = Some 2
> safediv 10 0
val it : int option = None
Option Types
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let isFortyTwo = function
| Some(42) -> true
| Some(_) | None -> false
> isFortyTwo (Some(43))
val it : bool = false
> isFortyTwo (Some(42))
val it : bool = true
Option Types
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Tuples
a “Group” of values
Often used for “multiple” return
values
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> let average (a, b) =
let sum = a + b
sum / 2.0
val average : float * float -> float
> average (10.0, 20.0)
val it : float = 15.0
Tuples
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> let divrem x y =
match y with
| 0 -> None
| _ -> Some(x / y, x % y)
val divrem : int -> int -> (int * int)
option
Tuples
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> divrem 100 20
val it : (int * int) option = Some (5, 0)
> divrem 6 4
val it : (int * int) option = Some (1, 2)
Tuples
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let greeting (name, language) =
match (name, language) with
| ("Steve", _) -> "Howdy, Steve"
| (name, "Engl") -> "Hello, “ + name
| (_, "French") -> "Bonjour!"
| _ -> "DOES NOT COMPUTE"
Tuples
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Records
Tuples with names values
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type website =
{ Title : string;
Url : string }
Records
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type website =
{ Title : string;
Url : string }
> let homepage = { Title = "Google"; Url
= "http://www.google.com" }
val homepage : website
Records
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> let homepage = { Title = "Wikibooks"; Url =
"http://www.wikibooks.org/" }
val homepage : website
> homepage.Title
val it : string = "Wikibooks"
> homepage.Url
val it : string = "http://www.wikibooks.org/"
Records
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type TransactionItem =
{ Name : string;
ID : int;
ProcessedText : string;
IsProcessed : bool }
let processItem item =
{ item with
ProcessedText = "Done";
IsProcessed = true }
Records
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type coords = { X : float; Y : float }
let getQuadrant = function
| { X = 0.0; Y = 0.0 } -> "Origin"
| item when item.X >= 0.0 && item.Y >= 0.0 -> "I"
| item when item.X <= 0.0 && item.Y >= 0.0 ->"II"
| item when item.X <= 0.0 && item.Y <= 0.0 ->"III"
| item when item.X >= 0.0 && item.Y <= 0.0 -> "IV"
Records
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Lists
ordered collection of values
immutable
linked list
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> let numbers = [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]
val numbers : int list
[1; 2; 3; 4; "cat"; 6; 7]
Lists
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> [1 .. 10]
val it : int list = [1; 2; 3; 4; 5; 6; 7; 8; 9; 10]
> [1 .. 2 .. 10]
val it : int list = [1; 3; 5; 7; 9]
> ['a' .. 's']
val it : char list
Lists
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let rec sum total = function
| [] -> total
| hd :: tl -> sum (hd + total) tl
Lists
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Set / Map
unordered collections
immutable
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> Set.empty.Add(1).Add(2).Add(7)
val it : Set = set [1; 2; 7]
let a = Set.ofSeq [ 1 .. 10 ]
let b = a
a.Add(12)
b.Add(13)
Set / Map
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let capitals =
[("Australia", "Canberra"); ("Canada", "Ottawa");
("China", “Beijing”);]
let canadaCapital = capitals.find("Canada")
Set / Map
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Discriminated Unions
tagged unions
finite set of choices
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type switchstate =
| On
| Off
let toggle = function
| On -> Off
| Off -> On
let main() =
let x = On
let y = Off
let z = toggle y
Discriminated Unions
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type switchstate =
| On
| Off
| Adjustable of float
Discriminated Unions
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Imperative
Programming
(impure!1!!)
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Mutability
Two types of mutability
re alias
&
references to same memory
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> let mutable x = 5
val mutable x : int
> x
val it : int = 5
> x <- 10
val it : unit = ()
> x
val it : int = 10
Mutability
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> let x = ref "hello";;
val x : string ref
> x;; (* returns ref instance *)
val it : string ref = {contents = "hello";}
> !x;; (* returns x.contents *)
val it : string = "hello"
> x := "world";; (* updates x.contents with a new value *)
val it : unit = ()
> !x;; (* returns x.contents *)
val it : string = "world"
Mutability
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> let cell1 = ref 7;;
val cell1 : int ref
> let cell2 = cell1;;
val cell2 : int ref
> cell1 := 10;;
val it : unit = ()
> !cell1;;
val it : int = 10
> !cell2;;
val it : int = 10
Mutability
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Typesafe (s)printf
sprintf "Hi, I'm %s and I'm a %s" "Juliet" “Scorpio"
sprintf "I'm %i years old" "kitty"
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Other
Control flow: if/then, for, while
Arrays: fixed size, mutable, fast
mutable Collections/Maps
Exceptions
Operators: define & overload
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Object Orientated
Programming
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OOP
Classes/Interfaces
Events: no magic
modules/namespaces
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Cool Stuff
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Unit of Measurement
additional dimension to
typesystem
statically checked
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Unit of Measurement
[]
type m (* meter *)
[]
type s (* second *)
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Unit of Measurement
[] type m (* meter *)
[] type s (* second *)
[] type kg (* kilogram *)
[] type N = (kg * m)/(s^2) (* Newtons *)
[] type Pa = N/(m^2) (* Pascals *)
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Unit of Measurement
> let distance = 100.0
let time = 5.0
let speed = distance / time;;
val distance : float = 100.0
val time : float = 5.0
val speed : float = 20.0
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Unit of Measurement
type triple<[] 'a> = { a : float<'a>; b :
float<'a>; c : float<‘a>}
{ a = 7.0; b = -10.5<_>; c = 0.5<_> }
val it : triple = {a = 7.0;
b = -10.5;
c = 0.5;}
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Computation Expressions
the easy monad
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Computation Expressions
let read_line() = System.Console.ReadLine()
let print_string(s) = printf "%s" s
print_string "What's your name? "
let name = read_line()
print_string ("Hello, " + name)
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Computation Expressions
let read_line(f) = f(System.Console.ReadLine())
let print_string(s, f) = f(printf "%s" s)
print_string("What's your name? ", fun () ->
read_line(fun name ->
print_string("Hello, " + name, fun () -> () ) )
)
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Computation Expressions
let getNum msg =
printf "%s" msg
match System.Int32.TryParse(System.Console.ReadLine()) with
| (true, n) when n >= 0 && n <= 100 -> Some(n)
| _ -> None
match getNum "#1: " with
| Some(x) ->
match getNum "#2: " with
| Some(y) ->
match getNum "#3: " with
| Some(z) -> Some(x + y + z)
| None -> None
| None -> None
| None -> None
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Computation Expressions
let bind(input, rest) =
match System.Int32.TryParse(input()) with
| (true, n) when n >= 0 && n <= 100 -> rest(n)
| _ -> None
let createMsg msg = fun () -> printf "%s" msg;
System.Console.ReadLine()
bind(createMsg "#1: ", fun x ->
bind(createMsg "#2: ", fun y ->
bind(createMsg "#3: ", fun z -> Some(x + y + z) ) ) )
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Computation Expressions
let bind(input, rest) =
rest(input())
let download (url : string) =
bind( (fun () -> new System.Net.WebClient()), fun webclient ->
bind( (fun () -> webclient.DownloadString(url)), fun html ->
bind( (fun () -> Regex.Matches(html, @"http://\S+") ), fun matches ->
printMsg ("Found " + matches.Count.ToString() + " links")
)
)
)
["http://www.google.com/"; "http://microsoft.com/"; "http://www.wordpress.com/";
"http://www.peta.org"] |> Seq.iter download
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Computation Expressions
let bind(input, rest) =
ThreadPool.QueueUserWorkItem(new WaitCallback(fun _ -> rest(input())))
let download (url : string) =
bind( (fun () -> new System.Net.WebClient()), fun webclient ->
bind( (fun () -> webclient.DownloadString(url)), fun html ->
bind( (fun () -> Regex.Matches(html, @"http://\S+") ), fun matches ->
printMsg ("Found " + matches.Count.ToString() + " links")
)
)
)
["http://www.google.com/"; "http://microsoft.com/"; "http://www.wordpress.com/";
"http://www.peta.org"] |> Seq.iter download
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Computation Expressions
let bind(input, rest) =
match System.Int32.TryParse(input()) with
| (true, n) when n >= 0 && n <= 100 -> rest(n)
| _ -> None
let createMsg msg = fun () -> printf "%s" msg;
System.Console.ReadLine()
bind(createMsg "#1: ", fun x ->
bind(createMsg "#2: ", fun y ->
bind(createMsg "#3: ", fun z -> Some(x + y + z) ) ) )
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Computation Expressions
> type MaybeBuilder() =
member this.Bind(x, f) =
printfn "this.Bind: %A" x
match x with
| Some(x) when x >= 0 && x <= 100 -> f(x)
| _ -> None
member this.Delay(f) = f()
member this.Return(x) = Some x
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Computation Expressions
let maybe = new MaybeBuilder()
let sugared =
maybe {
let x = 12
let! y = Some 11
let! z = Some 30
return x + y + z
}
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Computation Expressions
let maybe = new MaybeBuilder()
let desugared =
maybe.Delay(fun () ->
let x = 12
maybe.Bind(Some 11, fun y ->
maybe.Bind(Some 30, fun z ->
maybe.Return(x + y + z)
)
)
)
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Async Workflows
Based on Computation
Expressions
Used to run code in parallel
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Async Workflows
let extractLinks url =
async {
let webClient = new System.Net.WebClient()
printfn "Downloading %s" url
let html = webClient.DownloadString(url : string)
printfn "Got %i bytes" html.Length
let matches = Regex.Matches(html, @"http://\S+")
printfn "Got %i links" matches.Count
return url, matches.Count
};;
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Mailboxes
Erlang style message passing
reply channels
Async
Input queue
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Mailboxes
type msg =
| Incr of int
| Fetch of AsyncReplyChannel
let counter =
MailboxProcessor.Start(fun inbox ->
let rec loop n =
async { let! msg = inbox.Receive()
match msg with
| Incr(x) -> return! loop(n + x)
| Fetch(replyChannel) ->
replyChannel.Reply(n)
return! loop(n) }
loop 0)
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Mailboxes
> counter.Post(Incr 7);;
val it : unit = ()
> counter.Post(Incr 50);;
val it : unit = ()
> counter.PostAndReply(fun replyChannel -> Fetch
replyChannel);;
val it : int = 57
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TypeProviders
Compile time generated types
Based on arbitrary information
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TypeProviders
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TypeProviders
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Interested?
Go to:
fshrap.org
fsharpforfunandprofit.com
en.wikibooks.org/wiki/F_Sharp_Programming
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Thanks!