There's no charge for (functional) awesomeness

There’s no charge for
FUNCTIONAL
awesomeness

There’s no charge
for awesomeness…

OO History
1967 Simula
1971 Smalltalk
1983 C++
1985 Eiffel
1995 Design Patterns
1996 JDK 1.0
2000 Javascript
2002 C# 1.0

OO makes code understandable
by encapsulating moving
parts.
FP makes code understandable
by minimizing moving parts.
https://twitter.com/mfeathers/status/29581296216

What language you
wish you had
created?

Syntactic sugar
causes cancer of the
semicolon
Alan Jay Perlis

Functions are first
class citizens

Functions can be
declared anywhere

Can you do that in
Java or C#?

Functions that take
other functions as
parameters

Or return functions
as results

Passing the result to
the next function

public bool FindDragonWarrior(List<string> masters) 
{ 
var found = false; 
foreach (var master in masters) 
{ 
if (master == "Po") 
{ 
found = true; 
break; 
} 
} 
return found; 
}

Remove loop
private static bool TheNameIsPo(string master) 
{ 
return master == "Po"; 
} 
 
public bool FindDragonWarrior(List<string> masters) 
{ 
return masters.Any(TheNameIsPo); 
}

Local declaration
public bool FindDragonWarrior(IEnumerable<string> masters) 
{ 
var nameIsPo = new Func<string, bool>(m => m == "Po"); 
return masters.Any(nameIsPo); 
}

Multiple of 3 or 5
public void PrintMultiples(List<int> numbers) 
{ 
Func<int, bool> isMultiple = n => n % 3 == 0 || n % 5 == 0; 
numbers 
.Where(isMultiple) 
.Select(n => $"({n}) is multiple") 
.ToList() 
.ForEach(Console.WriteLine); 
}
let printMultiples numbers = 
let isMultiple n = n % 3 = 0 || n % 5 = 0 
numbers 
|> List.filter isMultiple 
|> List.iter (printf "(%d) Is multiple") 
F#

Lists, arrays,
dictionaries, sets,
etc

map
Converts each
element using a fn

reduce
Accumulates
elements applying a
fn

filter
Selects only the
elements matching

zip
Combines two lists
into pairs

Null References
The Billion Dollar
Mistake
Tony Hoare

Print First Master
public void PrintMasterName(List<Person> people) 
{ 
var master =
villagePeople
.FirstOrDefault(p => KFMaster.IsMaster(p.Name)); 
 
Console.Write($"The master name is {master.Name}"); 
}

Print First Master
public void PrintMasterName(List<Person> people) 
{ 
var master =
villagePeople
.FirstOrDefault(p => KFMaster.IsMaster(p.Name)); 
 
Console.Write($"The master name is {master?.Name}"); 
} 
Short
Circuit

TryFind first multiple
let printFirstMaster villagePeople = 
villagePeople 
|> List.tryFind (getName >> isMaster) 
|> Option.iter (getName >> printf "The fst master is %s") 
Only calls the function if
there is something

How many times
have you parsed an
int and failed?

What about a
customer that does
not have a
secondary address?

quicksort :: Ord a => [a] -> [a] 
quicksort [] = [] 
quicksort (p:xs) = (quicksort lesser) ++ [p] ++ (quicksort greater) 
where 
lesser = filter (< p) xs 
greater = filter (>= p) xs

Easy to extract
common
functionality

let fizzBuzz number = 
match number with 
| i when i % 3 = 0 && i % 5 = 0 -> "FizzBuzz" 
| i when i % 3 = 0 -> "Fizz" 
| i when i % 5 = 0 -> "Buzz" 
| _ -> number.ToString()

Replace function
with the
implementation

State introduces
time as a variable

Test data generation
and quick check

The Smartest tool
for agile project
management
http://smartview.io

amir@barylko.com
@abarylko
http://bit.ly/abarylkoslides
http://orthocoders.com
http://westerndevs.com

Resources
• InfoQ - StrangeLoop 2011 Language Panel http://bit.ly/1l2t5d2
• The joy of functional programming http://bit.ly/1LKTjJE
• Functional Programming: What? Why? When? http://bit.ly/1GVZJGN
• Oscon 2013 - Functional Thinking http://bit.ly/1kl2QOd
• F# for fun and profit http://bit.ly/1Pf1RLk

Photo Credit
• Under http://creativecommons.org/licenses/by/2.5/
• Jeremy Keith, Roast beef, http://flic.kr/p/TKUz
• Rob Campbell, Field of daisies, http://flic.kr/p/6QJjU4

There's no charge for (functional) awesomeness

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