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Learn Functional Programming in Haskell

Lambda Expressions

Explore the concept of lambda expressions in Haskell, which allow you to write anonymous functions without naming them. Understand how these expressions work with patterns and higher-order functions to create concise, flexible code. Learn to apply lambda expressions to solve problems and define functions on the fly, enhancing your functional programming skills in Haskell.

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In the previous lesson, we defined the higher-order function applyTwice and then used it on other functions like next or double.

Haskell
applyTwice :: (Int -> Int) -> Int -> Int
applyTwice f = f . f
double :: Int -> Int
double x = 2 * x
next :: Int -> Int 
next x = x + 1
main = do 
  print (applyTwice double 8)
  print (applyTwice next 7)

It can be annoying to define simple functions like double or next, especially if we just want to use them once in a higher-order function call.

If we just want to use a simple function temporarily, we do not need to give it a name. Instead, we can create an anonymous function using a lambda expression.

Introduction to lambda expressions

Lambda expressions are named after a mathematical system called Lambda calculus, which is the theoretical foundation of functional programming languages like Haskell. Lambda expressions start with the \ character, because it looks a little like the Greek letter lambda, requiring some imagination.

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