python-scala-functional

Python to Scala Functional Programming Translation

Higher-Order Functions

# Python
def apply_twice(f, x):
    return f(f(x))

def make_multiplier(n):
    return lambda x: x * n

double = make_multiplier(2)
result = apply_twice(double, 5)  # 20

// Scala
def applyTwice[A](f: A => A, x: A): A = f(f(x))

def makeMultiplier(n: Int): Int => Int = x => x * n

val double = makeMultiplier(2)
val result = applyTwice(double, 5)  // 20

Decorators → Function Composition

# Python
def log_calls(func):
    def wrapper(*args, **kwargs):
        print(f"Calling {func.__name__}")
        result = func(*args, **kwargs)
        print(f"Finished {func.__name__}")
        return result
    return wrapper

@log_calls
def add(a, b):
    return a + b

// Scala - function composition
def logCalls[A, B](f: A => B, name: String): A => B = { a =>
  println(s"Calling $name")
  val result = f(a)
  println(s"Finished $name")
  result
}

val add = (a: Int, b: Int) => a + b
val loggedAdd = logCalls(add.tupled, "add")

// Alternative: using by-name parameters
def withLogging[A](name: String)(block: => A): A = {
  println(s"Calling $name")
  val result = block
  println(s"Finished $name")
  result
}

Pattern Matching

# Python (3.10+)
def describe(value):
    match value:
        case 0:
            return "zero"
        case int(x) if x > 0:
            return "positive int"
        case int(x):
            return "negative int"
        case [x, y]:
            return f"pair: {x}, {y}"
        case {"name": name, "age": age}:
            return f"{name} is {age}"
        case _:
            return "unknown"

// Scala - pattern matching is more powerful
def describe(value: Any): String = value match {
  case 0 => "zero"
  case x: Int if x > 0 => "positive int"
  case _: Int => "negative int"
  case (x, y) => s"pair: $x, $y"
  case List(x, y) => s"list of two: $x, $y"
  case m: Map[_, _] if m.contains("name") =>
    s"${m("name")} is ${m("age")}"
  case _ => "unknown"
}

// Case class pattern matching (preferred)
sealed trait Result
case class Success(value: Int) extends Result
case class Error(message: String) extends Result

def handle(result: Result): String = result match {
  case Success(v) if v > 100 => s"Big success: $v"
  case Success(v) => s"Success: $v"
  case Error(msg) => s"Failed: $msg"
}