The document discusses functional programming concepts including: - Lambda calculus as the basis for functional programming and being equivalent to Turing machines. - Functional programming using functions to transform values rather than mutating state. - Examples of functional programming concepts like currying, composition, and working with collections in a functional way. - Origami, a library for implementing folds to work with different data types in a functional manner. - The benefits of functional programming like composability and creating abstractions. - The document encourages trying functional programming and provides examples in languages like Haskell.

1. FUNCTIONAL
PROGRAMMING
byAndražBajt
@edofic
availableat
slides.com/edofic/functional-programming

2. WHO AM I?
CS studentatFRI
developer atKoofr
STaaS provider startup

3. ENTROPY

4. HALTING PROBLEM

5. FIGHTING ENTROPY

6. OBJECT ORIENTATION
modelrealworld
objects allthe waydown
3 rules
design patterns

7. FUNCTIONS

8. LAMBDA CALCULUS
Alonso Curch 1930s
Equivalentto Turing Machine

9. LAMBDA CALCULUS
Verysimple
Abstraction
λx.y
Application
fx
Composability!

10. WHAT IS FP?

11. WHAT IS FP?
Programming with values
Using function to transform values

12. MY STORY
(roughly)
1. C(++)
2. C#
3. Java
4. Python
5. Scala
6. Haskell

13. WHY MOVE TO FP LAND?
Composability
Abstractions

14. GOT MATH?

15. EXAMPLES
functionapply(f,x){
<divstyle="text-align:center;"></div> returnf(x);
}
apply(function(x){returnx*2},1);
apply=(f,x)=>fx
apply((x)=>x*2,1)

16. CURRYING
apply=(f)=>(x)=>fx
apply((x)=>x*2)(1)

17. COMPOSITION
compose=(f)=>(g)=>(x)=>f(g(x))
foo=(x)=>x+1
bar=(x)=>x*2
f=compose(foo)(bar)
f(2)#5

18. COLLECTIONS
people=[
{name:"John",surname:"Doe",age:35},
{name:"Jane",surname:"Doe",age:49}
]
people
.filter((p)=>p.age>40)
.map((p)=>p.name+p.surname)
people.reduce(((total,p)=>total+p.age),0)/people.length

19. HELLO HASKELL WEB
main::IO()
main=scotty3000helloRoutes
helloRoutes::ScottyM()
helloRoutes=do
get "/" $html"hellothere"
get "/hello"$html"Helloworld"
post"/hello"$html"Hellopostman"
get "/hello/:name"$do
name<-param"name"
html$"Hello"`mappend`name

20. DSL
postUsersR::HandlerValue
postUsersR=do
Auth.adminOnly
user<-requireJsonBody
userIdMby<-runDB$insertUniqueuser
runValidationHandler$
("username","Userwiththesuppliedusernamealreadyexists")
`validate`(isJustuserIdMby)
getUsersUserR$fromJustuserIdMby

21. BUILDING A DSL
dataCommanda=Upa|Downaderiving(Eq,Show,Functor)
typeSequence=FreeCommand()
up,down::Sequence->Sequence
up=Free.Up
down=Free.Down
done::Sequence
done=Pure()
go=($done)
example=do
goup
goup
godown
goup

22. ORIGAMI
fsum::(Numa)=>Foldaa
fsum=Fold(+)0id
flen::(Numb)=>Foldab
flen=Fold(s_->s+1)0fromInteger
favg::(Fractionala)=>Foldaa
favg=(/)<$>fsum<*>flen
example=runfoldfavg[1,2,3]

23. ORIGAMI IMPLEMENTATION
For foldable things
dataFoldab=forallx.Fold(x->a->x)x(x->b)
instanceFunctor(Folda)where
f`fmap`Foldstepzeromap=Foldstepzero(f.map)
instanceApplicative(Folda)where
purea=Foldconst()(consta)
Foldf1z1m1<*>Foldf2z2m2=Foldfzmwhere
f(x1,x2)e=(f1x1e,f2x2e)
z=(z1,z2)
m(f,x)=(m1f)(m2x)
runfold::(Foldablet)=>Foldab->ta->b
runfold(Foldfzm)t=m$foldl'fzt

24. YOU SHOULD TRY IT
Libraries for your language
Learn a new language!

25. QUESTIONS