Real World Scalaz

1. REAL
W⊛RLD
SCALAZ
http://speakerdeck.com/u/jrwest/p/real-world-scalaz
changed talk title (“practical scalaz” by Chris Marshall http://skillsmatter.com/podcast/scala/practical-scalaz-2518)

2. “If you are thinking of using
Scalaz, stop now while you
still have your sanity"
* context: java devs learning scala
* source: http://zeroturnaround.com/blog/scala-sink-or-swim-part-1/#scalaz

3. “How does this help
you ship features or
improve your product?”
* context: commenting on the use of lenses
* source: https://twitter.com/#!/coda/status/167794305107361796)

4. “It will not immediately
help you write better
programs that are easy to
understand”
* hear/read this often
* source: http://zeroturnaround.com/blog/scala-sink-or-swim-part-1/#scalaz

5. “There are two types of
[libraries]: the ones people hate
and the ones nobody uses”
- unknown
* applies to scala too
* know correct attribution? contact me

6. HOW
&
WHY?
* those quotes pretty much boil down to these two questions:
* how: apply tools given by scalaz to real world problems? to handle human scale?
* why would we choose this solution over other ones?

7. @_jrwest
github.com/jrwest
blog.loopedstrange.com
* a little context before we talk about the “how & why?”

8. I
WORK @
* small team, < 15 engineers
* many have java bg, but not all, most w/ little to no scala experience
* most have oop bg, varying knowledge of FP topics

9. WE USE SCALA
{ a lot }
* 15+ public facing services supported by many other internal modules/libs
* most built on netty, also I/O bound
* originally java, now > 70% scala

10. libraryDependencies +=
“org.scalaz” %% “scalaz-core” % “6.0.3”
* almost all our services depend on scalaz
* usage levels and parts of scalaz used vary among services
* blocked on upgrading to 6.0.4 b/c of binary compatibility issues

11. SOME
EXAMPLES

12. JSON Mapping
def Fi
leMani
def re festJS
ad(jso ONR =
ma n: JVa new JS
nifest lue) = ONR[ Ap
NoId.a p I D= > F
field( pplyJS ileMan
jsonMa O N( ifest]
f i e l d( nifest {
)(json change K e y) ,
) LogEnt
} ryCach
edJson
} K e y)
* lift-json-scalaz (https://github.com/lift/framework/tree/master/core/json-scalaz)
* validationnel applicative, error accumulation = better user-facing errors & debugging
* composition

13. S @-@ A / State[S,A]
for
{
mbE
_ xis
<- ts
_ man <-
<- ife man
} y cha stF ife
iel nge ile stF
d m Log s - ile
bEx Ent = p s m
ist ryF ath emb
s ile er
s - pat
=? h
(pa
th,
mbE
xi sts
>|
fal
se
| t
rue
)
* easy manipulation of highly nested case classes (ex: file manifests)
* better implementation hiding
* rich libraries (e.g. MapLens, SetLens, & provided state actions)

14. sideEffect.pure[IO]
ble ,X]
[ Thr owa = {
io n NEL in g]) _))
al i dat st [ Str mai n] (
X ]=V : Li mDo
y pe V[ s (ke ys [Cu sto
t tch K ey
t .fe tch ain ]])
def fe buc ke tom Dom
ap ( Cus
ke y s.m pti on[
qu e nce ce[ V,O
.se seq uen
(_.
. map
}
* can’t guarantee purity, can delineate impurity
* examples: storing data in riak, uploading files to s3 and phonegap build svc
* composition of IO makes side-effecting code much more reusable

15. Kle
]
i sli
]
OptionW[A] Tree[A]
F[_
[M
[_]
le[
,A, Pure[P[_]
B] ]
ab
MAB[M[
_],A,B]
ld
Bind[Z[ [A]
_ ]] ro
Fo
Ze t[ A]
Tra ty Lis
ver Identity ] NonEmp
p [ A
e [T s u
Fun [_]] r o
ctor mig Appl
[F[_] Se y[A[_
] MA[ M[_ ],A] ]]
* we make use of a lot more as well
* data structures like Validation and NonEmptyList
* most type classes and “enrichments”

16. ITS NOT ALL OR NOTHING
* shades of grey, not black and white
* scalaz is really many libraries, use the parts you want
* we started using “encrichments” and some data structures, grew from there
--
original image: http://www.chicagonow.com/chicago-tough/files/2012/03/chipsallin.jpg

17. MAKE BORDERS
* don’t abuse scala’s flexibility & power
* toss pure/impure code into a salad bowl & mixing is a bad idea
* define borders where pure code meets impure code
--
original image: http://media.nowpublic.net/images//59/4/59455eabd625a15e2afb583dcfbb27ce.jpg

18. Public Interface
Implementation
Dependency Calls
* your code can be pure
* public interface is the border, it runs IO, throws exceptions, etc
* existing libraries probably aren’t pure -- many are java after all

19. Outside World
Business Logic
* communicate with clients via HTTP
Data Access
* the most important part -- your code -- make pure*
* perform side-effects like talk to database, read/write files, etc

20. Impure
Pure
Impure
* “the sandwich” - common pattern in our code
--
original image: http://fastfood.ocregister.com/files/2010/05/ice-cream-sandwich1.jpg

21. :)
* code has become much more DRY/modular and as a result more unit testable
* concurrent code becomes “simpler” to reason about when pure
* FP makes reasoning about bugs simpler, narrow down cause faster

22. :(
* scala hardsips: bin. compatability problems, tooling deficiencies, type inference limits
* import scalaz._; import Scalaz._ adds a lot of clutter in the current scope
* lack of docs/related content (in Scala!)

23. scalaz7
* not currently used in our production systems but one or two of my side projects
* much better for teaching (explicit type class instance usage -- w/o syntax ext.)
* addresses some of the issues we have like importing “the scalaz world”

24. “SCALE”?

25. “Human Scale”
* the complexity comments may be FUD, but that does not mean there is not stuff to learn here
* how do we help new employees learn scala & scalaz?

26. HIRE PEOPLE WHO
WANT TO LEARN
* hiring from all backgrounds instead of hiring a “scala or java developer” is much easier
* those people need to be open to exploring and learning new tech/methods

27. Shared Resources
* easy win, shares effort in finding good resources
* dropbox full of downloaded papers and books purchased by the company
* internal talks available on github

28. * code review/pull requests
LEARN TOGETHER
* face to face discussion on a whiteboard
* team talks on fridays, any one can attend, anyone can talk, neither mandatory

29. ON YOUR OWN
* RTFC -- in the end it all just code
* apply what you know, this is what really makes you learn it
* internal talks mostly make you aware of it, give you starting point, application is key

30. ITS NOT ALL OR NOTHING
* focus on understanding a part of the library
* break that part down, use it in the repl in a few cases (w/ a few types, examples, etc)
* as you learn more about each part and then more parts the bigger picture emerges
--
original image: http://www.chicagonow.com/chicago-tough/files/2012/03/chipsallin.jpg

31. Learn You a
??
* not necessary
* understanding syntax, basics can be useful while learning concepts until scala docs fill out
--
haskell logo: http://www.haskell.org/wikistatic/haskellwiki_logo.png

32. ASK #scalaz
FOR HELP

33. BREAK
RULES
* you may hear things you cannot do, “validation is not a monad”
* ignore and explore yourself -- these are the real learning opportunites
* understand how to implement validation monad and why no error accum. happens

34. PAYING
UPFRONT
* of course this have some upfront cost
* so does writing tests and similarly a good balance pays off

35. L3
L2
L1
A3
Level
A2
A1
Up
* scalaz covers most advanced features in scala language
* great guide for library and code design (to an extent). Scalaz guys have done serious amount of research in this regard

36. Thanks!
talk recap slide

37. SOME RESOURCES
• Atlassian’s Typeclassopedia - http://typeclassopedia.bitbucket.org
• Apocalisp Blog - http://apocalisp.wordpress.com/
• “Functional Programming in Scala” MEAP - http://manning.com/bjarnason/
• Eric Torreborre’s Blog - http://etorreborre.blogspot.com/
• StackMob Engineering Blog - http://www.stackmob.com/category/engineering/
• Learn You a Scalaz (my WIP, about to undergo major rework) -
https://github.com/jrwest/learn-you-a-scalaz
• Chris Marshall’s “Practical Scalaz” Talk - http://skillsmatter.com/podcast/scala/
practical-scalaz-2518