Scala Functional Programming Cheat Sheet

Covers Scala functions and currying, pattern matching, functional collection operations, and core functional programming concepts like immutability.

2 PagesIntermediateApr 10, 2026

Functions & Currying

Function values, higher-order functions, and partial application.

scala

// Function values and higher-order functionsval square: Int => Int = x => x * xdef applyTwice(f: Int => Int, x: Int): Int = f(f(x))applyTwice(square, 3)   // => 81// Partial application / curryingdef add(a: Int)(b: Int): Int = a + bval addFive = add(5) _addFive(10)   // => 15// Immutable valuesval name: String = "Scala"   // val is immutable; var is mutable

Pattern Matching

Destructuring case classes and matching with guards.

scala

sealed trait Shapecase class Circle(radius: Double) extends Shapecase class Rectangle(width: Double, height: Double) extends Shapedef area(shape: Shape): Double = shape match {  case Circle(r)       => math.Pi * r * r  case Rectangle(w, h) => w * h}// Matching with guardsdef describe(n: Int): String = n match {  case 0          => "zero"  case x if x > 0 => "positive"  case _          => "negative"}

Functional Collections

map, filter, fold, and for-comprehensions.

scala

val numbers = List(1, 2, 3, 4, 5)val doubled = numbers.map(_ * 2)          // List(2, 4, 6, 8, 10)val evens = numbers.filter(_ % 2 == 0)    // List(2, 4)val total = numbers.foldLeft(0)(_ + _)    // 15val sum = numbers.sum                     // 15// for-comprehensionval pairs = for {  x <- List(1, 2)  y <- List("a", "b")} yield (x, y)// List((1,a), (1,b), (2,a), (2,b))

Core FP Concepts

Foundational ideas behind Scala's functional style.

Immutability- val bindings and immutable collections (List, Vector) are the default; prefer them over var and mutable collections
case class- Auto-generates equals, hashCode, toString, and copy(); ideal for immutable data
Option[T]- Represents an optional value as Some(value) or None, avoiding null and NullPointerException
Higher-order functions- Functions that take or return other functions, e.g. map, filter, and foldLeft
for-comprehension- Syntactic sugar over flatMap/map/withFilter for chaining monadic operations like Option, List, and Future
Pattern matching- match expressions destructure case classes and sealed traits, with exhaustiveness checked at compile time

Pro Tip

Use sealed traits with case classes for algebraic data types — the compiler warns on non-exhaustive match expressions, catching missing cases at compile time instead of runtime.

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