An Introduction to F#

Sushant Bhatia

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aboutdev@gmail.com

Why learn F#?

OverviewTour of F# in Visual Studio 2011

Fundamentals of F#

Functional Programming

Examples

F# in Visual Studio 2011DEMO

Fundamentals of F#

Signature Name Description Example

Unit Unit ()

int, float Concrete Type 10, 6.04

‘a, ‘b Generic Type

‘a -> ‘b Function Type fun x -> x + 1

‘a * ‘b Tuple Type Ordered collection of values

(1, 2), (“ten”, “soup”)

‘a list List Type List of values [1; 2; 3], [1 .. 3]

‘a option Option Type Optional value Some(3), None

Core Types

Default -> anonymous module

Nest Modules

Namespace

Modules & Namespaces

Pass results of first function to second

Benefit Chain functions togetherType inference

Pipe Forward

[1 .. 10] |> List.map (fun x -> x * x) |> List.iter (printfn "%i")

Series of rules that will execute if a pattern matches the input.

Switch on Steroids

Pattern Matching

Type

1 of a set of possible values

Used for complex data structures

Discriminated Unions

Functional Programming

What is Functional Programming?

A function is a rule that associates to each x from some set X of values, a unique y from another set Y of values. If f is the name of the function,

y = f ( x )

f : X → Y

Functional programming is a programming paradigm that treats computations as the evaluation of mathematical functions and avoids state and mutable data.

[Wikipedia]

All programs and procedures are functions and clearly distinguish incoming values from outgoing values

There are no variables or assignments – variables are replaced by parameters

There are no loops – replaced by recursive calls

The value of a function depends only on the value of its parameters and not on the order of evaluation or the execution path that led to the call

Functions are first-class values (viewed as values themselves, computed by other functions and can be parameters to functions)

[Programming Languages. Kenneth C Louden]

1. First Class Functions

2. Higher Order Functions

3. Pure Functions

4. Recursion / Tail Recursion

5. Currying

1. First Class Functions

a) Bind an identifier to a function definition

let sqr = fun n -> n * n

b) Store functions in data structures

let aTuple = (sqr, fun n -> n + n) let aList = [sqr, fun n -> n + n]

2. Higher Order Functions

a) Pass function as an argumentlet data = List.map (fun n -> n * n) [ 1; 2; 3; 4; ]

b) Return function as value of function

let sqrList = let funSqr = fun lst -> List.map (fun a -> a * a) lst funSqr

3. Pure Functions

a) No Side Effects / Referential transparency

b) Caching optimizations (memoization)

c) No Data Dependency = order of execution is independent and can be parallel (thread-safe)

4. Recursion / Tail Recursion

a) Iteration through recursive invocationlet rec factorial x = if x <= 1I then 1I else let recResult = factorial (x-1I) let result = x * recResult result

b) Tail recursion – Accumulatorslet factorialTail x = let rec tailRecFact x acc = if x <= 1I then acc else tailRecFact (x-1I) (acc * x) tailRecFact x 1I

5. Currying

let add x y = x + y

let addToTen = add 10

addToTen 5

Demo

1. Type Provider – Netflix

2. Units of Measure

3. Async / Parallel

Examples – Project Euler

How to Learn F#

1. Programming F# - Chris Smith2. Beginning F# - Robert Pickering3. Expert F# - Don Syme

4. http://blogs.msdn.com/b/dsyme5. http://en.wikibooks.org/wiki/Programming:F_Sharp6. http://projecteuler.net/ 7. http://fdatamining.blogspot.com/2009/12/f-online-

videos.html8. http://www.tryfsharp.org/Tutorials.aspx9. http://fssnip.net/

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