Template-Oriented-Programming (TOP) to Ship Faster

Template-Oriented-Programming to Ship
Faster
/
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@GopalAkshintala
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overfullstack.github.io
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I'm
Gopal S Akshintala
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Software Engineer @ Salesforce
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@GopalAkshintala
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overfullstack.github.io/about-me/
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@GopalAkshintala
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Disclaimer*
• Basics First
• More Why & How, less What
• Don't stress yourself on low-level details. Just sit-
back and relax
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• You may keep your mics on
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(Silence is intimidating
than FPH)
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@GopalAkshintala
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Why FP?
• Surely, not because it feels cool
• Changes the way you think about coding.
• Code like Maths equations and deravations.
• These are Design patterns too.
• Concise
• High Quality (Bug free)
• Expressive
• Shared Vocab
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@GopalAkshintala
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Ok! What are we going to do
today?
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@GopalAkshintala
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What is Monomorphic?
• Number sorting algorithms
• How can we reuse it for sorting strings?
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@GopalAkshintala
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What is Polymorphic?
• Types of Polymorphism
• Subtype with Inheritance
• Parametric with Generics E.g., List
• Ad-hoc Polymorphism with Typeclasses
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@GopalAkshintala
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Typeclasses
• What is the heart of all our sorting algorithms?
• Comparator 8 It's a typeclass
• What is the connection between a DataType and a
Typeclass?
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@GopalAkshintala
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Comparator
val appleComparator = Comparator { apple1, apple2 4
apple1?.let { first 4
apple2?.let { second 4
first.weight.compareTo(second.weight)
} ?: 1
} ?: 0
}
listOf(Apple(3), Apple(1), Apple(2)).sortedWith(appleComparator)
I J [Apple(weight=1), Apple(weight=2), Apple(weight=3)]
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@GopalAkshintala
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Let's create a Simple Typeclass
interface AdderTC {
fun add(a: AddableT, b: AddableT): AddableT
8 AddableT type should be a member of AdderTC type class by implementing all its methods.
fun addAll(addables: List) =
addables.reduce { acc, i C add(acc, i) }
}
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@GopalAkshintala
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AdderTC
To make Int a member of AdderTC:
val intCombine = object : AdderTC {
override fun add(a: Int, b: Int) = a + b
}
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@GopalAkshintala
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AdderTC
To make String a member of AdderTC:
val stringCombine = object : AdderTC {
override fun add(a: String, b: String) = a + b
}
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@GopalAkshintala
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AdderTC
println(intCombine.addAll(listOf(1, 2, 3)))
: ; 6
println(stringCombine.addAll(listOf("a", "b", "c")))
: ; abc
This is Ad-hoc Polymorphism
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@GopalAkshintala
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Before moving-on, any
Questions
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@GopalAkshintala
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Another Monomorphic Example
Email Validation
fun validateEmail(email: String): Either =
if (email.contains("@", false)) {
if (email.length B 250) {
Unit.right()
} else {
ValidationError.EmailMaxLength(250).left()
}
} else {
ValidationError.DoesNotContain("@").left()
}
This is stuck with Fail fast
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@GopalAkshintala
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Another Monomorphic Example
private fun validateEmailErrorAccumulation(email: String): Either, Unit> {
val errorList = mutableListOf()
if (!email.contains("@", false)) {
errorList.add(ValidationError.DoesNotContain("@"))
}
if (email.length > 250) {
errorList.add(ValidationError.EmailMaxLength(250))
}
return if (errorList.isNotEmpty()) errorList.left() else Unit.right()
}
This is stuck with Error Accumulation
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@GopalAkshintala
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How to make it Polymorphic?
• What makes-up the heart of this algorithm?
• The Effect of being Valid/Invalid
• The Effect of combining all validation errors
• How to abstract them out?
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@GopalAkshintala
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The Polymorphic magic
The Orchestration
fun ValidatorAE.validateEmailWithRules(email: String): KindtupledN(
contains(email, "@"),
maxLength(email, 250)
).handleErrorWith { raiseError(it) }
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@GopalAkshintala
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The Fail-Fast
private fun validateEmailFailFastX(email: String): Either, Tuple2failFast().run {
validateEmailWithRules(email).fix()
}
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@GopalAkshintala
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The Error Accumulation
private fun validateEmailErrorAccumulationX(email: String): Validated, Tuple2errorAccumulation().run {
}
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@GopalAkshintala
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Λrrow made the magic possible
arrow-kt.io
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@GopalAkshintala
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Some Intimidating Terminology
The Typeclass Arsenal
• Functor
• Monad
• Applicative
• ApplicativeError
• 3(many more)
DataTypes such as Option, Either, Validated implement these interfaces.
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@GopalAkshintala
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Typeclasses : DataTypes
Type class Combinators List Option Either
EitherApplicati
ve
EitherApplicati
veError
Validated
ValidatedApplic
ative
ValidatedApplic
ativeError
Functor map, lift ✓ ✓ ✓ ✓
Monad flatMap,
flatten
✓ ✓ ✓ ✓
Applicative pure, ap ✓ ✓ ✓ ✓
ApplicativeErro
r
raiseError,
catch
✕ ✓ ✓ ✓
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@GopalAkshintala
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Functor
Is any Datatype that implements a map operation
source
source Functors, Applicatives, And Monads In Pictures | adit.io
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@GopalAkshintala
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Functor
source
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@GopalAkshintala
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Functor
source
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@GopalAkshintala
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Functor
listOf("a", "b", "c").map { it.toUpperCase() }
Option("info").map { it.toUpperCase() }
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@GopalAkshintala
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Monad
Is any Datatype that implements a flatMap operation
source
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@GopalAkshintala
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Monad
source
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@GopalAkshintala
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Monad
source
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@GopalAkshintala
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Monad
Monad is used for Dependent operations
Option("userName").flatMap { getFirstName(it) }
fun getFirstName(userName: String) : Option = Option("firstName")
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@GopalAkshintala
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Applicative
Is anything that has an apply
source
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@GopalAkshintala
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Applicative
• But why do you want to put a function inside a box?
• You can do some interesting things, to combine two
wrapped values, using an operation called product.
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@GopalAkshintala
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Applicative
Applicative is used for Independent operations
fun getFirstName(userName: String) : Option = Option("firstName")
fun getLastName(userName: String) : Option = Option("lastName")
fun getFullName(userName: String) = getFirstName(userName).product(getLastName(userName))
.map { names: Tuple2 C "${names.a} ${names.b}" }
G H Some(firstName lastName)
product internally calls apply, by converting its wrapped argument to a wrapped function, but
let's not get into details now.
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@GopalAkshintala
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Applicative
It's all Maths!
println(None.product(Some(3)))
3 5 None
println(Some(3).product(None))
3 5 None
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@GopalAkshintala
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Meditative
Well, it's not a typeclass, let's pause,
take a deep breathe and revise.
Coz, we are gonna shift gears!
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@GopalAkshintala
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ApplicativeError
It is same as Applicative, with an E! Ya it has a
raiseError(e: E) method.
Either.applicativeError().raiseError("Dark")
: < Left(Dark)
Option.applicativeError().raiseError(Unit)
: < None
• applicativeError() is just a companion method on the DataType to get
ApplicativeInstance
• When raiseError(e) is called, the Datatype transitions into the dark side.
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@GopalAkshintala
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ApplicativeError
Why is this important? Any guesses, how this raiseError() can help
our validation?
• The Effect of being Valid/Invalid - This can be taken care by
the Left and Right states and raiseError takes care of the
transition.
• The Effect of combining all validation errors - This can be
taken care by the product.
• But what about Strategy switching between Fail-Fast and Error-
Accumulation?
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@GopalAkshintala
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ApplicativeError
We have ready made type classes for these strategies:
EitherApplicativeError : ApplicativeError, L>
ValidatedApplicativeError : ApplicativeError, E>
• Again, let's not get into the details, but let's
understand the more important HOW?
• Hint: product implementation in both these typeclasses
is going to make the difference
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@GopalAkshintala
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EitherApplicativeError
Product Matrix
Invalid Valid
Invalid Invalid Invalid
Valid Invalid Product
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@GopalAkshintala
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ValidatedApplicativeError
Product Matrix
Invalid Valid
Invalid Accumulate Errors Add First Error
Valid Add First Error Product
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@GopalAkshintala
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Controlling Strategy with Effect
The Strategies
fun failFast(): FailFast = Either.applicativeError()
fun errorAccumulation(): ErrorAccumulation = Validated.applicativeError(NonEmptyList.semigroup())
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@GopalAkshintala
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The Entry point of execution
private fun validateEmailFailFastX(email: String): Either, Tuple2failFast().run {
}
private fun validateEmailErrorAccumulationX(email: String): Validated, Tuple2errorAccumulation().run {
}
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@GopalAkshintala
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The Product
fun ValidatorAE.validateEmailWithRules(email: String): KindtupledN( F Product
contains(email, "@"),
maxLength(email, 250)
).handleErrorWith { raiseError(it) }
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@GopalAkshintala
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The Validations
private fun ValidatorAE.contains(email: String, needle: String): Kind =
if (email.contains(needle, false)) just(email)
else raiseError(ValidationError.DoesNotContain(needle).nel())
private fun ValidatorAE.maxLength(email: String, maxLength: Int): Kind =
if (email.length H maxLength) just(email)
else raiseError(ValidationError.EmailMaxLength(maxLength).nel())
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@GopalAkshintala
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Done!
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@GopalAkshintala
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Please Feedback
DM on twitter @GopalAkshintala
Email me - [email protected]
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@GopalAkshintala
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Show me the Code
github.com/overfullstack/ad-hoc-poly
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@GopalAkshintala
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Let's Slack together!
bit.ly/overfullstack-slack
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@GopalAkshintala
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Thanks!
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@GopalAkshintala
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Template-Oriented-Programming (TOP) to Ship Faster

Template-Oriented-Programming (TOP) to Ship Faster

Gopal S Akshintala

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