Still fascinating how Smalltalk implements if/then/else. Basically it goes like this (in pseudo-Swift):

smalltalkbooleans.swift

class BooleanClass {
  void ifTrue(_ trueHandler: () -> Void, else falseHandler: () -> Void)
}

class TrueBooleanClass {
  void ifTrue(_ trueHandler: () -> Void, else falseHandler: () -> Void) {
    trueHandler()
  }
}

class FalseBooleanClass {
  void ifTrue(_ trueHandler: () -> Void, else falseHandler: () -> Void) {
    falseHandler()
  }
}

let True = TrueBooleanClass()
let False = FalseBooleanClass()

let result: BooleanClass = someFunctionThatReturnsTrueOrFalse()

result.ifTrue( { in
  print("The result was True")
}, else: { in
  print("The result was False") }
)