F# (F Sharp)An Introductory Look

By Kody Myers

History“Mathematicians stand on each others' shoulders and computer scientists stand on each others' toes.”

- Richard Hamming, 1968 Turing Award recipient

Lambda Calculus (λ-calculus)

• A formalism for representing functions.

• Formulated by Alonzo Church in the 1930s.

• Formed the basis of functional programming.

Early Functional Languages

• Lisp – 1958

• ISWIM (“If you See What I Mean”) – 1966

• Metalanguage (ML) – 1973

• Caml – 1985

• Haskell - 1990

"There are only two kinds of programming languages: those people always bitch about and those nobody uses.”

- Bjarne Stroustrup, Creator of C++

“Why Nobody Uses Functional Languages”

• Article appeared in the ACM SIGPLAN Notices newsletter in 1998 by Philip Wadler.

• Wadler was one of the principal designers of Haskell.

[…] there are a large number of factors that hinder the widespread adoption of functional languages. To be widely used, a language should support interlanguage working, possess extensive libraries, be highly portable, have a stable and easy to install implementation, come with debuggers and profilers, be accompanied by training courses, and have a good track record on previous projects.

-- Philip Wadler

Don Syme

• Principal Researcher at Microsoft Research, Cambridge, UK.

• Was working on generics for C# for the .NET Framework.

• Tasked with finding a functional language that would be a good fit with .NET.

Haskell.NET?

We had a go doing Haskell for .NET. We actually got a long way in doing that, but in the end there is quite a lot of dissonance between Haskell and .NET.

- Don Syme

Okay, How About OCaml.NET, Then?

• OCaml: Objective Caml

• Dialect of Caml.

• Descendent of Metalanguage (ML).

F# 1.0 – May 2005

• Functional programming

• Discriminated unions

• Records

• Tuples

• Pattern matching

• Type abbreviations

• Object programming

• Structs

• Signature files

• Scripting files

• Imperative programming

• Modules (no functors)

• Nested modules

• .NET Interoperability

F# 2.0 – April 2010

• Active patterns

• Units of measure

• Sequence expressions

• Asynchronous programming

• Agent programming

• Extension members

• Named arguments

• Optional arguments

• Array slicing

• Quotations

• Native interoperability

• Computation expressions

F# 3.0 – August 2012

• Type providers

• LINQ query expressions

• CLIMutable attribute

• Triple-quoted strings

• Auto-properties

• Provided units-of-measure

Present Day

F# 3.1 – October 2013

• Named union type fields

• Extensions to array slicing

• Type inference enhancements

**Specification not yet finalized

Currently Active Keywords

abstract

and

as

assert

base

begin

class

default

delegate

do

done

downcast

downto

elif

else

end

exception

extern

false

finally

for

fun

function

global

if

in

inherit

inline

interface

internal

lazy

let

let!

match

member

module

mutable

namespace

new

not

null

of

open

or

override

private

public

rec

return

return!

select

static

struct

then

to

true

try

type

upcast

use

use!

val

void

when

while

with

yield

yield!

Inactive Keywords From OCaml

asr

land

lor

lsl

lsr

lxor

mod

sig

Reserved Keywords for Future Use

atomic

break

checked

component

const

constraint

constructor

continue

eager

event

external

fixed

functor

include

method

mixin

object

parallel

process

protected

pure

sealed

tailcall

trait

virtual

volatile

Introducing your“let-saber”“A more elegant weapon for a more civilized age.”

- Obi Wan Kenobi, Star Wars: A New Hope

“let” Us Begin

let hello = “Hello World!”

let pi = 3.1415926

let isRunning = false

let numList = [1 .. 10]

let vehicle = (2013, “Ford”, “Explorer”, true)

let userId = System.Guid.NewGuid()

Wow, Those Puns Were Terrible

• Yeah, you’re probably right.

• Time to lose these boring slides for awhile.

Advantages of F#

• Highly readable, especially for developers who are already with functional languages and .NET programming.

• Highly writeable, especially developing with the help of the Visual Studio IDE.

• Highly reliable, thanks to the tried and heavily-tested libraries of the .NET Framework.

• Moderately portable to other, non-Windows platforms, thanks to the Mono project.

Disadvantages of F#

• Functional languages require an uncomfortable adjustment to the way programmers normally think about problems.

• Sacrifices a measure of performance in favor of reliability.

• Hasn’t garnered a comparable amount of confidence as the other more well-established languages of the .NET Framework.

• Practical solutions are limited to very specific class of problems.

The Future: F# 4.0+

• Printf on unitized values

• Extension property initializers

• Non-null provided types

• Class names as functions

• Static parameters for provided methods

• Printf interpolation

• Extended #if grammar

• Support for 'fixed'

• Tailcall attribute

• Multiple interface instantiations

• Optional type args

• Params dictionaries

A Sampling of Practical Applications

• Unit conversion

• Power generation load balancing and scheduling

• Insurance risk engine

• Game rules engine

• Website click prediction

• Forensic image comparison

• Genome sequencing

• Game player ranking

let isFSharpUseful = true

Source: http://fsharp.org/testimonials/

Suggested Resources

• Try F# – tryfsharp.org

• The F# Software Foundation – fsharp.org

• F# for fun and profit – fsharpforfunandprofit.com