WHATWHATWHATWHATWHATWHAT

WHAT

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WHAT

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HASKELLHASKELLHASKELLHASKELLHASKELLHASKELL

HASKELL

HASKELL

HASKELL

HASKELL

HASKELL

HASKELL

HASKELL

HASKELL

HASKELLHASKELLANDVICEVERSA

WHATWHATWHATWHATWHATWHAT

WHAT

WHAT

WHAT

WHAT

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WHATWHATJAVACANLEARNFROM

HASKELLHASKELLHASKELLHASKELLHASKELLHASKELL

HASKELL

HASKELL

HASKELL

HASKELL

HASKELL

HASKELL

HASKELL

HASKELL

HASKELLHASKELLANDVICEVERSA

Nick Linker @nick_linkerNick Linker @nick_linker

EXAMPLES( )

Anchor Applikativ Assertible Borders Beautiful_DestinationsAnchor Applikativ Assertible Borders Beautiful_DestinationsByteAlly Capital_Match ByteAlly Capital_Match Chordify CircuitHub CommonwealthChordify CircuitHub Commonwealth

Bank DigitalX Elsen Extensibl Facebook FP_CompleteBank DigitalX Elsen Extensibl Facebook FP_CompleteFPInsight Front_Row_Education Helium_SystemsFPInsight Front_Row_Education Helium_SystemsHooky,_Inc Infinipool Iris_Connect Hooky,_Inc Infinipool Iris_Connect Keera_StudiosKeera_Studios

Kite_&_Lightning Least_Fixed LexisNexis_Risk_SolutionsKite_&_Lightning Least_Fixed LexisNexis_Risk_SolutionsLumi_Guide Lumi_Guide Madriska_Inc. Microsoft MidrollMadriska_Inc. Microsoft Midroll

MyFansDemand Picus_Security Pivot_Cloud PreziMyFansDemand Picus_Security Pivot_Cloud PreziRheo_Systems Scoompa Scrive Scyfy_Technologies SilkRheo_Systems Scoompa Scrive Scyfy_Technologies SilkSimplyRETS Snowdrift.coop SimplyRETS Snowdrift.coop Soostone Stack_BuildersSoostone Stack_BuildersStandard_Chartered Stitcher Suite_Solutions SumAllStandard_Chartered Stitcher Suite_Solutions SumAll

Swift_Navigation Systor_Vest thoughtbot Tree.isSwift_Navigation Systor_Vest thoughtbot Tree.isTsuru_Capital Turing_Jump Tsuru_Capital Turing_Jump UpHere VaryWell VFILESUpHere VaryWell VFILESVirtual_Forge Wagon Wellposed Well-Typed ZaloreVirtual_Forge Wagon Wellposed Well-Typed Zalore

SOURCE

HASKELLIS...FunctionalPureLazy (by default)With advanced type systemGHC

25 years old, but moves fastlast release 2016-05-21

WHATJAVACANLEARNExpressive syntaxPurityExpressive Type SystemGHCi (REPL)...

EXPRESSIVESYNTAX

EXPRESSIVESYNTAX(1)sizexs=loopxs0whereloop[]acc=accloop(_:xs)acc=loopxs(acc+1)

--Usagesize[1,2,3]

EXPRESSIVESYNTAX(2)

The type of size aboveThe type of size above

In generalIn general

size::[t]->Integer--?

size::Numa=>[t]->a--actualltype

f::(C1a)=>a->b->c->d->e(fa1)::b->c->d->e(fa1b1)::c->d->e(fa1b1c1)::d->e(fa1b1c1d1)::e

EXPRESSIVESYNTAX(3)

A spherical program in vacuumA spherical program in vacuum

moduleMy.Foowhere

importData.Timehiding(Day)

foo::IO()foo=doct<-getCurrentTimeputStrLn("UTCtime="++showct)

PURITY

PURITY(1)

Seriously, what about file system? Network? Random?Seriously, what about file system? Network? Random?

PURITY(2)

They have the same Java type.They have the same Java type.

However, these functions are not interchangeable!However, these functions are not interchangeable!

longgetLength(Stringstr){returnstr.length();}

longgetFileLength(Stringpath){returnnewFile(path).length();}

PURITY(3)

In Haskell they'd have different types:In Haskell they'd have different types:

(Monad tutorial goes here...)(Monad tutorial goes here...)

getLength::String->Integer

getFileLength::String->IOInteger

EXPRESSIVETYPES

EXPRESSIVETYPES(1)

NEWTYPES

Milliseconds vs secondsUsername vs passwordPaths vs contentsIndices

In Haskell wrapping can be free!In Haskell wrapping can be free!

//callthisasrunScript("sql/RunStuff.sql")ResultrunScript(Stringscript){...}

EXPRESSIVETYPES(2)

NEWTYPES

Looks like a separate type, but low-level representation isLooks like a separate type, but low-level representation isthe same.the same.

--typesaferunScriptnewtypePath=PathString

runScript::Path->IOResult

EXPRESSIVETYPES(3)

ALGEBRAICDATATYPESANDPATTERNMATCHINGdataVoiddataX=XdataY=YIntTextXdataZ=ZxX|ZyYdataDay=Mon|Tue|Wed|Thu|Fri|Sat|SundataUser=User{id::Int,name::Text,day::Day}

EXPRESSIVETYPES(4)

ALGEBRAICDATATYPESANDPATTERNMATCHING

Constructing values and matchingConstructing values and matching

letz=Zy(Y123"Hey"X)letu1=User{id=1,name="Vasya",day=Mon}letu2=User2"Petya"Tueletd=Sat

wd::Day->Stringwdd|d`elem`[Mon,Tue,Wed,Thu]->"Workingday"wdd|d`elem`[Sat,Sun]->"Weekendday"wdFri->"Friday"

caseu1ofUseridnameday->...

EXPRESSIVETYPES(5)

TYPECLASSES

Typeclasses decouple the declaration that a typeTypeclasses decouple the declaration that a typeimplements an interface from the declaration of the typeimplements an interface from the declaration of the type

itselfitself

DataType Eq Ord ToJSON FromJSON

Apple

Orange

More on More on Intefaces vs TypeclassesIntefaces vs Typeclasses

EXPRESSIVETYPES(5)

TYPECLASSES

Typeclasses decouple the declaration that a typeTypeclasses decouple the declaration that a typeimplements an interface from the declaration of the typeimplements an interface from the declaration of the type

itselfitself

DataType Eq Ord ToJSON FromJSON

Apple Eq

Orange

More on More on Intefaces vs TypeclassesIntefaces vs Typeclasses

EXPRESSIVETYPES(5)

TYPECLASSES

Typeclasses decouple the declaration that a typeTypeclasses decouple the declaration that a typeimplements an interface from the declaration of the typeimplements an interface from the declaration of the type

itselfitself

DataType Eq Ord ToJSON FromJSON

Apple Eq Ord

Orange

More on More on Intefaces vs TypeclassesIntefaces vs Typeclasses

EXPRESSIVETYPES(5)

TYPECLASSES

Typeclasses decouple the declaration that a typeTypeclasses decouple the declaration that a typeimplements an interface from the declaration of the typeimplements an interface from the declaration of the type

itselfitself

DataType Eq Ord ToJSON FromJSON

Apple Eq Ord

Orange Eq

More on More on Intefaces vs TypeclassesIntefaces vs Typeclasses

EXPRESSIVETYPES(5)

TYPECLASSES

Typeclasses decouple the declaration that a typeTypeclasses decouple the declaration that a typeimplements an interface from the declaration of the typeimplements an interface from the declaration of the type

itselfitself

DataType Eq Ord ToJSON FromJSON

Apple Eq Ord

Orange Eq ToJSON

More on More on Intefaces vs TypeclassesIntefaces vs Typeclasses

EXPRESSIVETYPES(5)

TYPECLASSES

Typeclasses decouple the declaration that a typeTypeclasses decouple the declaration that a typeimplements an interface from the declaration of the typeimplements an interface from the declaration of the type

itselfitself

DataType Eq Ord ToJSON FromJSON

Apple Eq Ord

Orange Eq ToJSON

Lemon Eq Ord ToJSON FromJSON

More on More on Intefaces vs TypeclassesIntefaces vs Typeclasses

EXPRESSIVETYPES(6)

TYPECLASSES

EXPRESSIVETYPES(7)

ITISPOSSIBLETOCHECKATCOMPILETIME

Arrays boundsOpen vs closed filesNested transactionsGuaranteed closing resourcesREST endpointsAndtestareavailabletoo!

ANDMANYMORE

WHATHASKELLCANLEARN

Flat learning curveIntellij IDEAStackoverflow...

HASKELLLEARNINGCURVE

LEARNINGCURVE(1)

HASKELLLEARNINGCURVE,COMPARISON

LEARNINGCURVE(2)

THINGSTOLEARNINHASKELL

1. Syntax, functions from Prelude2. Monads3. Concurrency & parallelism, STM4. Libraries

1. Monad transformers2. Free monads, recursive schemes3. Arrows, Lens, Type families4. Type safe DSLs, TH5. Whateveryouwant

LEARNINGCURVE(4)

COMPAREWITHC++

Thenewbookreleased,thetranslationofThenewbookreleased,thetranslationoftheC++17StandardDrafttoRussian.888theC++17StandardDrafttoRussian.888

pages.Yousay,Haskellistoocomplex?pages.Yousay,Haskellistoocomplex?Okay...Okay...@dshevchenko@dshevchenko

INTELLIJIDEA

There is no analog for Haskell.There is no analog for Haskell.

There are plugins/extensions forThere are plugins/extensions for

AtomVimEmacsSublime

However, Haskell's stepping debugger (GHCi) is notHowever, Haskell's stepping debugger (GHCi) is notuniversal.universal.

STACKOVERFLOWANDDOCS

For Java it is easy to find examples and goodFor Java it is easy to find examples and gooddocumentation.documentation.

For HaskellFor Haskell

The documentation is often poorNeeded to look into the libraries' codeFortunately I could ask my colleagues directly.

OURCASE

OURCASE

1. There were communication problems inside the team2. There was a split between haskellers and javaists3. ...Despite the pretty good quality of the services itself4. The productivity would not save us :-/

OURCASE

1. There were communication problems inside the team2. There was a split between haskellers and javaists3. ...Despite the pretty good quality of the services itself4. The productivity would not save us :-/

One should take the social aspects into account One should take the social aspects into account during theduring theintroduction of the new technologies.introduction of the new technologies.

SO?

ISITWORTHTOUSEHASKELLINPRODUCTION?

1. Only if all team members are eager to learn Haskell2. Maybe for some separate task, e.g. compiler3. I believe one can grow a team of Haskellers4. .. but cannot easy switch team to Haskell (you cannot

force people to learn)

Examples: GHC, Corrode, Elm, PureScript, Agda,Examples: GHC, Corrode, Elm, PureScript, Agda,Kaleidoscope, PandocKaleidoscope, Pandoc

Haskell is not for Production and Other Tales, Katie MillerHaskell is not for Production and Other Tales, Katie Miller and and VideoVideo SlidesSlides

ISITWORTHTOLEARNHASKELL?(1)

YES!1. to get a new way of thinking and to push the boundaries2. to know how to structure things without inheritance3. to know the alternatives to the buzzwords: DDD,

Anemic, Patterns, IOC, SOLID, DI, ...4. to finally understand monads

ISITWORTHTOLEARNHASKELL?(2)

OO is full of design problemsOO is full of design problems

is hard to get it done righta lot of buzzwordsas opposite to algorithms there is no clear criteriawhether is one solution better than anothercow.eat(grass)grass.beEatenBy(cow)field.eatingInteraction(cow,grass)

ISITWORTHTOLEARNHASKELL?(2)

QUESTIONS?