functional programming (let's fall back in love with programming)

Functional programmingLet’s fall back in with programming

Sudipta Mukherjee

What’s Functional ProgrammingIt’s telling the computer what to get done, not how to get it done

Top 5 Reasons for considering

Functional Programming

Composability: Let’s you compose solutions for complex problems easily

Lazy Evaluation: Enables you to benefit from Lazy evaluation

Immutability: Being able to write code that is side effect free

Parallelizable: You get easy parallelization options

Declarative: Lets you write very expressive code so readability increases.

And you get more done with less code.

I strongly recommend that you don’t try to remember these. Once you are

familiar with functional programming, these will seem obvious.

Functional Programming

Implementations

C# by LINQ

Rx.NET (Functional programming for Windows Events)

F# ( A succinct, multi-paradigm programming, functional first programming

language from Microsoft Research)

fsharp.org

Lambdas in C++ 11

http://www.cprogramming.com/c++11/c++11-lambda-closures.html

http://www.youtube.com/watch?v=5t-_wI7nFdU

LINQ Clone for C++

http://cpplinq.codeplex.com/

Who is using Functional Programming

Microsoft’s latest Functional Programming Language F# is widely accepted.

http://fsharp.org/testimonials/

Objective of this Talk

Ignite interest for Functional Programming (a.k.a FP)

We shall see how FP can help us remove boilerplate code

Provide some initial resources to get you started

Examples and Demos today will use LINQ

If people are interested, we can have a F# session later.

A 15 floor hotel gets built in 2 days!

Can we build software that fast and

flawless ?

We can.If we have the right tools.

Oh yes, and the

requirement should

be frozen.

A little comparison

House building

Complex by nature

Amendments are expensive

Mature Industry

Oh, I bet

Creating Software

Complex

Amendments are expensive

Mature Industry?

I doubt

We don’t have

enough generic

building blocks

How many times you have written code

for any of these situations

Finding if there is a match in a

collection

Finding all the elements that

matches a given condition

Finding the count of elements in a

collection that matches a set of

given conditions

Aggregating values of a collection

in a given way

Creating a histogram of all values

Creating a lookup table for all

values in a collection

Concatenating several collections

into one as in merge sort

Finding if there is only one

instance of something in a

collection

…. And so many other such trivial

things.

Boilerplate code

Functional ProgrammingCan save us from writing the same boilerplate code time and again.

How? By wrapping boilerplate codes into several functions that eventually

becomes the vocabulary of the programmers.

How many times you have written code

for any of these situations

Finding if there is a match in a

collection

Finding all the elements that

matches a given condition

Finding the count of elements in a

collection that matches a set of

given conditions

Aggregating values of a collection

in a given way

Creating a histogram of all values

Creating a lookup table for all

values in a collection

Concatenating several collections

into one as in merge sort

Finding if there is only one

instance of something in a

collection

…. And so many other such trivial

things.

Boilerplate code

Any

Where

Count

Aggregate

ToLookup

Concat

Single

LINQPadThe tool used in demo

The best C#/VB/F# snippet editor/compiler ever

Download from http://www.linqpad.net/

Use Dump() method to see anything. You can dump anything

DateTime.Today.Dump();

(new List<int>(){1,2,3}).Dump();

DemoLet’s see some example using LINQ

Now little bit of theoryJust enough so that you see the point

Programming with functionsIt’s just high school math. Reloaded.

Simple functions

f(x) = x + 1g(x) = x + 2z(x) = x == 0

Composite functions/higher order function

g.f(x) = g(f(x)) = g(x+1) = x + 1 + 2 = x + 3

You have been already doing it

Excel Formulae

=SUM(AVERAGE(A1:A10))

LINUX/Powershell Pipes

ls | sort –r

Get-Process | Sort-Object id

Function Types

Statistical

Gives a statistic of a collection.

Generators

Generates something

Filters

Filters a collection

Projectors

Projects a collection as something

T [ ]

Generators

Generates something out of nothing.

Filters

T [ ]T [ ]

T

Runs a predicate/filter for all elements of the given collection and

returns one or more matching entries.

Projectors

U [ ]T [ ]

T and U can be same

Projects a list to another of same or other type using a mapping

function

Statistical

T [ ] Boolean

T [ ] Numeric

Finds some statistical values for the given collection.

Func<> and Action<> (C# Specific)

What type is this function ?

Loop to LINQ

Thank You So Much!! Send queries to sudipto80@yahoo.com