Article about functional programming in kotlin #133

patrickwilmes · 2025-11-12T14:47:30Z

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abishekanthony07

All in all the Blog is really expressive and on point!
I have mostly added suggestions to Kotlin code. Feel free to challenge them!
Thank you Patrick!

abishekanthony07 · 2025-11-13T08:00:05Z

src/articles/kotlin-functional-programming/index.md

+> **"Every tool is a lens. The more lenses you collect, the more truth you see."**
+
+Most experienced developers live and breathe **object-oriented programming (OOP)**.
+We design systems in terms of entities, behaviors, and hierarchies; we reason about state, lifecycle, and encapsulation. It works beautifully—until it doesn’t.


Minor

Write each sentence in a new line. Helps to pin-point findings.

abishekanthony07 · 2025-11-13T08:04:44Z

src/articles/kotlin-functional-programming/index.md

+You find yourself wishing you could express _what_ you want, without micromanaging _how_ it happens.
+
+That’s where **functional programming (FP)** enters — not as a rival philosophy, but as a complementary one. FP isn’t about writing math puzzles or memorizing category theory.
+It’s a practical way to make logic predictable, composable, and testable.


Suggested change

It’s a practical way to make logic predictable, composable, and testable.

It’s a practical way to make business logic predictable, composable, and testable.

abishekanthony07 · 2025-11-13T08:13:55Z

src/articles/kotlin-functional-programming/index.md

+It’s a practical way to make logic predictable, composable, and testable.
+Instead of modeling _objects that do things_, FP focuses on _functions that transform data_.
+
+This article helps experienced OOP developers understand and apply FP concepts using **Kotlin**, without detouring into abstract theory. But the same principles and techniques can


Suggested change

This article helps experienced OOP developers understand and apply FP concepts using **Kotlin**, without detouring into abstract theory. But the same principles and techniques can

This article helps experienced OOP developers understand and apply FP concepts using **Kotlin**, without detouring into abstract theory.

abishekanthony07 · 2025-11-13T08:14:21Z

src/articles/kotlin-functional-programming/index.md

+Instead of modeling _objects that do things_, FP focuses on _functions that transform data_.
+
+This article helps experienced OOP developers understand and apply FP concepts using **Kotlin**, without detouring into abstract theory. But the same principles and techniques can
+also be applied to any Java code base (Java 8+).


Suggested change

also be applied to any Java code base (Java 8+).

The same principles and techniques can also be applied to any Java 8+ code base.

abishekanthony07 · 2025-11-13T08:20:05Z

src/articles/kotlin-functional-programming/index.md

+```kotlin
+fun <T, R> Collection<T>.mapToSet(mappingFunc: (T) -> R): Set<R> {
+    val targetSet = mutableSetOf<R>()
+    forEach { targetSet.add(mappingFunc(it)) }


Suggested change

forEach { targetSet.add(mappingFunc(it)) }

this.forEach { targetSet.add(mappingFunc(it)) }

just for clarity ;)

maybe shortly explain that the scope changes in extension function to the type which we extend ;)

abishekanthony07 · 2025-11-13T08:35:51Z

src/articles/kotlin-functional-programming/index.md

+class OrderService {
+    fun processOrder(order: Order): Result<Order> =
+        validateOrder(order)
+            .map { applyDiscount(it, 0.1) }


Suggested change

.map { applyDiscount(it, 0.1) }

.map { applyDiscount(0.1) }

abishekanthony07 · 2025-11-13T08:36:08Z

src/articles/kotlin-functional-programming/index.md

+    fun processOrder(order: Order): Result<Order> =
+        validateOrder(order)
+            .map { applyDiscount(it, 0.1) }
+            .flatMap { saveOrder(it) } // Side effect wrapped in Result


Suggested change

.flatMap { saveOrder(it) } // Side effect wrapped in Result

.flatMap { save() } // Side effect wrapped in Result

abishekanthony07 · 2025-11-13T08:37:35Z

src/articles/kotlin-functional-programming/index.md

+}
+```
+
+A backend service might model its domain in OOP but express its data transformations functionally—clean logic, explicit effects.


Suggested change

A backend service might model its domain in OOP but express its data transformations functionally—clean logic, explicit effects.

A backend service might model its domain in OOP, but express its data transformations functionally—clean logic, explicit effects.

abishekanthony07 · 2025-11-13T08:40:01Z

src/articles/kotlin-functional-programming/index.md

+When OOP gives us _nouns_, FP gives us _verbs_. Together they form the full grammar of software.
+
+The goal isn’t _purity_, but _clarity_.  
+Start small: use `val` instead of `var`, extract pure functions, embrace `map`, `filter`, and `flatMap`.  


Suggested change

Start small: use `val` instead of `var`, extract pure functions, embrace `map`, `filter`, and `flatMap`.

Start small: focus on **immutability** (`val` instead of `var`), extract pure functions, and embrace `map`, `filter`, and `flatMap`.

abishekanthony07 · 2025-11-13T08:41:35Z

src/articles/kotlin-functional-programming/index.md

+
+The goal isn’t _purity_, but _clarity_.  
+Start small: use `val` instead of `var`, extract pure functions, embrace `map`, `filter`, and `flatMap`.  
+Over time, you’ll find that FP principles don’t just make your code safer—they make it _simpler_.


Suggested change

Over time, you’ll find that FP principles don’t just make your code safer—they make it _simpler_.

Over time, you’ll find that FP principles don’t just make your code safer—they also make it _simpler_.

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Article about functional programming in kotlin #133

Article about functional programming in kotlin #133

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	It’s a practical way to make logic predictable, composable, and testable.
	It’s a practical way to make business logic predictable, composable, and testable.

	This article helps experienced OOP developers understand and apply FP concepts using Kotlin, without detouring into abstract theory. But the same principles and techniques can
	This article helps experienced OOP developers understand and apply FP concepts using Kotlin, without detouring into abstract theory.

	also be applied to any Java code base (Java 8+).
	The same principles and techniques can also be applied to any Java 8+ code base.

	forEach { targetSet.add(mappingFunc(it)) }
	this.forEach { targetSet.add(mappingFunc(it)) }

	.flatMap { saveOrder(it) } // Side effect wrapped in Result
	.flatMap { save() } // Side effect wrapped in Result

	A backend service might model its domain in OOP but express its data transformations functionally—clean logic, explicit effects.
	A backend service might model its domain in OOP, but express its data transformations functionally—clean logic, explicit effects.

	Start small: use `val` instead of `var`, extract pure functions, embrace `map`, `filter`, and `flatMap`.
	Start small: focus on immutability (`val` instead of `var`), extract pure functions, and embrace `map`, `filter`, and `flatMap`.

	Over time, you’ll find that FP principles don’t just make your code safer—they make it _simpler_.
	Over time, you’ll find that FP principles don’t just make your code safer—they also make it _simpler_.

Article about functional programming in kotlin #133

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