3 FP Concepts: Recursion, List Comprehensions and Monads

1. 3 FP Concepts
Recursion, List comprehensions and Monads
@diego_pacheco  about.me/diegopacheco

2. 3 FP Concepts
Recursion
List Comprehensions
Monads

3. Recursion

4. Recursion
 Function defined inside a function
 Function calling it-self
 Defining an infinite set of objects by a finite
statement (Recursion Power by Wikipedia)
 Same behavior as loop, for, while, etc…

5. Recursion

6. List Comprehensions

7. List Comprehensions
 Syntactic construct based on lists
 Inspired by math: set comprehensions
 Expressions on lists, powerful stuff!

8. List Comprehensions

9. Monads

10. Monads => NO State on a world FULL of
State, Looks nonsense!? WTF?

11. FP/Haskell are against state? Hell No!
It’s all about discipline state…

12. How to Deal with state without global
shared state variables ?

13. Workaround => Truck Food as Monad !!!
(Abstraction)

14. Monads
 Deal with side-effects in a functional way
 Mathematical construct
 Without monads PURE FP would be nuts
 Functional able todo IO
 Good to Control tracking of things
 Similar to AOP Interceptors
 Function Composition: LINQ, Unix Pipes
 You can build environments that support exactly
the features that you want (Scala Option[A])
 Encapsulating two things:
 control flow (Maybe, Error, List, Continuation, parser monads)
 state propagation (State, Reader, Writer, IO)

15. Monads as types/class (>>=), OOP!?

16. Monads have laws…
its not just type/classes
Make possible assumptions about the
type/class and his behavior.
1. Left Identity (apply function to value)
return x >>= f (the same as) f x
sample: return 3 >>= (x -> Just (x+100000))
2. Right Identity (value to feed return)
m >>= return (the same as) m
sample: [1,2,3,4] >>= (x -> return x)
3. Associativity (no matter how nested chain)
(m >>= f) >>= g (the same as) m >>= (x -> f x >>= g)
sample: return (0,0) >>= landRight 2 >>= landLeft 2 >>= landRight 2

17. Monads
>>= (bind)

18. Monads

19. https://github.com/diegopacheco/functional-society

20. 3 FP Concepts
Thank You!
Obrigado!
Higher Order Functions, Lambda and Currying
@diego_pacheco  about.me/diegopacheco