Functional Reactive And Arrow-kt

Pure functional programming using Kotlin

Transcript

1. Functional Reactive and
   Arrow-kt
   Lightning Talk
   Jan 29 2018
   github.com/
   ersin-ertan
   

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2. Android/Java/Kotlin can functional w libs, code
   google/autovalue - immutable value-type
   google/dagger - compile-time dependency injection
   evant/auto-value-lens - modify composed values
   twitter/
   inline fun tryOrDefault(default: T, block:() ->T) =try { block() } catch(e:Exception) default }
   

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3. What is Arrow?
   Companion to Kotlin's standard library enabling pure functional programming
   Not a new concept, but new to Kotlin/Android
   Pure Functional is to domain modeling as Kotlin native is to platform
   

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4. What is Pure Functional?
   Programming process
   To model behaviour, are verbs/actions
   Only operate on input, and provide output
   Limited to functions scope
   

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5. How do we work with Pure Functional?
   Reduce behaviour
   Use domain vocabulary
   Use immutable objects, state change requires a new object
   fun addOne(a:A) = A(a.num + 1)
   

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6. Why Pure Functions?
   Everyone can call it
   Is simple business rules
   Easy to understand
   Easy to test
   Compose larger behaviours via smaller ones
   

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7. How do we compose?
   Be generic, use parametric types and functions
   Parametric types are in containers
   List
   List is an Abstract Data Type(ADT)
   

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8. Can my ADT compose/operate with your ADT?
   Yes
   

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9. Can my ADT compose/operate with your ADT?
   Yes, because we use Arrow’s abstractions
   They are generic container classes specifically to do this
   Arrow is modeling the domain of Category Theory
   

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10. What is Category Theory?
    The mathematics of composition/morphisms
    Conceptual framework for structure/system of structures
    Has laws(associativity, identity)
    Arrows types(abstractions) obey these laws
    Operate on sets
    

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11. Algebraic Data Types
    Not operating on values, but types
    sealed class MyBoolean{
    fun and(other:MyBoolean):MyBoolean
    class MyTrue:MyBoolean(){...}
    class MyFalse:MyBoolean(){...}
    }
    

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12. when(myBoolean){
    is MyTrue -> {...}
    is MyFalse -> {...}
    }
    Compiler verifies type of our Algebraic Data Types
    Verified when passing as function input/output
    Now have referential transparency
    

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13. Why?
    Logic is explicit, type safe/constrained
    The domain model is pure/encoded within the type system
    Project’s domain models(types/algebra) are a superset of the Arrows types/algebra
    We have a common language to describe computation
    

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14. Why?
    Logic is explicit, type safe/constrained
    The domain model is pure/encoded within the type system
    Project’s domain models(types/algebra) are a superset of the Arrows types/algebra
    We have a common language to describe computation
    The domain algebra is decoupled from the projects implementation
    Ad-hoc polymorphism
    

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15. Why?
    Logic is explicit, type safe/constrained
    The domain model is pure/encoded within the type system
    Project’s domain models(types/algebra) are a superset of the Arrows types/algebra
    We have a common language to describe computation
    The domain algebra is decoupled from the projects implementation
    Ad-hoc polymorphism (soon-ish KEEP#87)
    

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16. Usage and To Solve
    fun
    myDomainBehaviour(a:AbstractionForSequentialComputation,
    b:AbstractionForComputationContainingDependencies,
    c:(AbstractionForParallelComputation) ->
    AbstractionForValidation):AbstractionThatReturnsOfMyType> {
    abstractionForIoOperation(abstractionForReactiveImplementation)(abstraction
    ForFrontEndUiEventRegardlessOfPlatform)
    

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17. Where?
    http://arrow-kt.io/
    https://github.com/arrow-kt/arrow
    https://gitter.im/arrow-kt/Lobby
    https://github.com/Kotlin/KEEP/pull/87
    compile 'io.arrow-kt:arrow-effects-rx2:0.6.0' // optional
    compile 'io.arrow-kt:arrow-effects-kotlinx-coroutines:0.6.0' // optional
    http://arrow-kt.io/docs/quickstart/blogs/ and in depth presentations
    http://arrow-kt.io/docs/quickstart/projects/
    https://github.com/JorgeCastilloPrz/ArrowAndroidSamples Functional Architecture
    github.com/
    ersin-ertan
    

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