Functional Programming

1. Functional programming
Let’s fall back in with programming
Sudipta Mukherjee

2. What’s Functional Programming
It’s telling the computer what to get done, not how to get it done

3. 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.

4. 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/

5. Who is using Functional Programming
 Microsoft’s latest Functional Programming Language F# is widely accepted.
 http://fsharp.org/testimonials/

6. 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.

7. A 15 floor hotel gets built in 2 days!

8. Can we build software that fast and
flawless ?

9. Oh yes, and the
requirement should
be frozen.
We can.
If we have the right tools.

10. 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

11. 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

12. Functional Programming
Can save us from writing the same boilerplate code time and again.

13. How?
By wrapping boilerplate codes into several functions that eventually
becomes the vocabulary of the programmers.

14. How many times you have written code
for any of these situations
 Finding if there is a match in a
collection
Any
 Finding all the elements that
matches a given condition
Where
 Finding the count of elements in a
collection that matches a set of
given conditions
Count
 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.
Aggregate
Boilerplate code
ToLookup
Concat
Single

15. LINQPad
The 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();

16. Demo
Let’s see some example using LINQ

17. Now little bit of theory
Just enough so that you see the point

18. Programming with functions
It’s just high school math. Reloaded.
Simple functions
f(x) = x + 1
g(x) = x + 2
z(x) = x == 0
Composite functions/higher order function
g.f(x) = g(f(x)) = g(x+1) = x + 1 + 2 = x + 3

19. You have been already doing it
 Excel Formulae
 =SUM(AVERAGE(A1:A10))
 LINUX/Powershell Pipes
 ls | sort –r
 Get-Process | Sort-Object id

20. Function Types
 Statistical
 Gives a statistic of a collection.
 Generators
 Generates something
 Filters
 Filters a collection
 Projectors
 Projects a collection as something

21. T [ ]
Generators
Generates something out of nothing.

22. Filters
Runs a predicate/filter for all elements of the given collection and
returns one or more matching entries.
T [ ] T [ ]
T

23. Projectors
Projects a list to another of same or other type using a mapping
function
T [ ] U [ ]
T and U can be same

24. Statistical
Finds some statistical values for the given collection.
T [ ]  Boolean
T [ ] Numeric

25. Func<> and Action<> (C# Specific)
 What type is this function ?

26. Loop to LINQ

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