Functional programming brings benefits like easy to read, understand and test code due to its use of pure functions without side effects. It employs techniques like lambda calculus, higher order functions and immutability which make concurrency easier and reduce bugs. While initially seen as weird and theoretical, many large tech companies are now using FP for its ability to make programming and software development simpler and more productive.

1. MAKING LIFE EASIER WITH JUST
TYPES AND FUNCTIONS
CHANDAN SINGH
ThoughtWorks

3. the curse of functional programming!
once you understand it well enough, you lose the
ability to explain it to others...

4. why (typed) functional programming?
it looks cool on your résumé!

5. complaints against FP?
it’s weird,
impractical,
why do it when OO/Procedural just works?
theoretical/academic nonsense,
no one really does it

6. who’s doing FP?
Facebook,
Twitter,
LinkedIn,
Microsoft,
Chef,
Many banks...

7. There’s something about the
culture of software that has
impeded the use of
specification. We have a
wonderful way of describing
things precisely that has been
developed over the last couple
of millennia, and it’s called
Mathematics.
-- Leslie Lamport,
Turing Award Winner, 2013.

8. what does FP bring to the table?
good code
easy to read
easy to understand
easy to test
easy to maintain

9. insanity!
doing the same thing over
and over again, and
expecting different
results!
--Albert Einstein
launchMissiles();
=> destroys enemy units
launchMissiles();
=> throws OutOfMissilesException

10. what is FP?
lambda calculus
id(x) = x
x -> x
square_sum(x, y) = x * x + y * y
(x, y) -> x * x + y * y
x -> (y -> (x * x + y * y))

11. confused? let’s make it simple!
pure functions, no side effects
also, higher order functions

12. what’s a function?
a mapping,
each input mapped to exactly
one output,
domain co-domain

13. functions are inherently typed
meaningful mappings,
transformation rules => constraints,
capture constraints precisely

14. public Integer square(Integer n)
{
n = n * n;
return n;
}
mutation, side effecting => impure
public Integer square(Integer n)
{
return n * n;
}
no side effect, does only one thing => pure

15. impure stuff
setters,
void/unit methods,
in-memory updates,
random()

16. what’s wrong with impure stuff?
contextual dependency
state changes
order of execution is important
far too much guessing to be done

17. stop talking, show some code!

18. so why is this FP suddenly a rage?
concurrency ...
immutability, ftw!

19. code, code, more code...

20. so again, why (typed) FP?
making things easier,
programming with less effort,
developer happiness!

21. thank you!