val message : string

Full name: index.message
val printfn : format:Printf.TextWriterFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.printfn

F# CAMP

Introduction to Functional Programming

Tomasz Heimowski

Agenda

  1. Introduction to the workshop series
  2. What is Functional Programming
  3. Why Functional Programming
  4. Examples of functional concepts in C#

Introduction to the workshop series

Aim

  • Learn F# language
  • Discover Functional Programming concepts
  • Find out how to start using F# at work
  • Have fun
  • No prior F# / Functional Programming knowledge required - we're starting from scratch

Format

  • 4 meetings in July, each thursday
    • first - introductory talk (this one, ~45min)
    • 2nd, 3rd, 4th - combined talk + workshops (45+90 ~= 2-2.5h)
  • Each workshop will cover concepts from the preceding talk
  • If it rolls out nicely, there'll be a continuation of the series

Books (soon in our library)

Real World Functional Programming

real-world-functional-programming-cover

https://amzn.com/1933988924

F# Deep Dives

fsharp-deep-dives

https://amzn.com/1617291323

Structure and Interpretation of Computer Programs

https://amzn.com/0262510871

Purely Functional Data Structures

https://amzn.com/0521663504

An Introduction to Functional Programming Through Lambda Calculus

https://amzn.com/0486478831

Source for presentations

Presentation made by FsReveal

Prerequisites

Install F# for workshops

http://fsharp.org/use/windows/

If you have VS 2015, but no F# installed:

https://github.com/Microsoft/visualfsharp/issues/544#issuecomment-221505568

What is Functional Programming

Overview of the various programming paradigms according to Peter Van Roy

Functional programming is a style of programming that emphasizes the evaluation of expressions, rather than execution of commands. The expressions in these languages are formed by using functions to combine basic values.

Hutton

State

  • In Object-Oriented Programming we combine data with behavior
  • In Functional Programming we separate out data from behavior

Statements vs Expressions

  • Imperative style:
    • Statements
    • Commands
  • Declarative style:
    • Expressions
    • Functions

https://twitter.com/mariofusco/status/571999216039542784

imperatywny vs funkcyjny

Brief history

  • First functional language: LISP (1958)
  • ML (1970) - generic functions
  • OCaml (1996) - hybrid language
  • F# came live with VS 2010

Other important FP languages: Haskell, Erlang, Scala, Clojure

Hello world F#

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let message = "Hello world!"
printfn "%s" message

Why Functional Programming

Prevent unwanted side effects

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public int TestA()
{
    return 5 + 6;
}

public int TestB()
{
    return Sum(5, 6);
}

public int Sum(int a, int b)
{
    var result = a + b;
    Console.WriteLine("Result is {0}", result);
    return result;
}

"Referential transparency"

Make code more testable

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public decimal Salary(decimal hourlyRate, decimal hours)
{
    if (System.DateTime.Now.DayOfWeek = DayOfWeek.Saturday)
    {
        return hourlyRate * hours * 1.5M;
    }
    else if (System.DateTime.Now.DayOfWeek = DayOfWeek.Sunday)
    {
        return hourlyRate * hours * 2.0M;
    }
    else 
    {
        return hourlyRate * hours;
    }
}

"Isolation"

Generalize common patterns

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public int Sum(int[] numbers)
{
    var sum = 0;
    for (int i = 0; i < numbers.Length; i = i+1)
    {
        sum = sum + numbers[i];
    }
    return sum;
}

public int Product(int[] numbers)
{
    var product = 1;
    for (int i = 0; i < numbers.Length; i = i+1)
    {
        product = product * numbers[i];
    }
    return product;
}

Discover right "abstractions"

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class Rectangle 
{
    public Rectangle(int width, int height)
    {
        this._width = width;
        this._height = height;
    }
}

// ok or not ok?
class Square : Rectangle 
{
    public Square(int width) : Rectangle(width, width)
    { 
    }
}

Trying to be too Object-Oriented

Inhale concurrency

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class ThreadSafeOrNot
{
    static readonly object _monitor;
    Dictionary _field;

    public void Manipulate()
    {
        lock (_monitor)
        {
            DoSomething(_field);
        }
    }
}

Twitter reactions

twitter-reed

Twitter reactions

twitter-james

Twitter reactions

twitter-paulmichael

Twitter reactions

twitter-marius

Examples of functional concepts in C#

Immutability

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class Age
{
    readonly int _year;
    Age(int year)
    {
        _year = year;
    }
    void ChangeYear()
    {
        //_year = 1967; // Compile error if uncommented.
    }
}

Generics

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public class Stack<T> {
    readonly int m_Size; 
    int m_StackPointer = 0;
    T[] m_Items;
    public Stack(int size) {
        m_Size = size;
        m_Items = new T[m_Size];
    }
    public void Push(T item) {
        m_Items[m_StackPointer] = item;
        m_StackPointer++;
    }
    public T Pop() {
        m_StackPointer--;
        return m_Items[m_StackPointer];
    }
}

Lambda functions + LINQ

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public string OddStringsTogether(IEnumberable<int> numbers)
{
    return
        numbers
            .Where(n => n % 2 == 1)         // filter
            .Select(n => n.ToString())      // map
            .Aggregate((n1,n2) => n1 + n2); // fold
}

Async / Await

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async Task<int> AccessTheWebAsync()
{ 
    HttpClient client = new HttpClient();
    Task<string> getStringTask = 
        client.GetStringAsync("http://msdn.microsoft.com");
    DoIndependentWork();
    string urlContents = await getStringTask;
    return urlContents.Length;
}

Summary

  • In this series of workshops we'll learn basics of F# and Functional Programming
  • FP is mainly about "evaluation of expressions, rather than execution of commands"
  • FP helps you write better code
  • F# is a functional-first language available on .NET
  • Multi-paradigm languages (e.g. C#) also make use of functional bits
  • It's worth to learn F# / FP - even if you just want to improve how you write code in non-FP languages

Next Week

Basic concepts of Functional Programming

talk + workshop

  • Immutability
  • Recursion
  • Expression-oriented programming