Lambda functions

Lambda functions are anonymous (or nameless) functions. This means that they can be applied without having an explicit declaration, i.e. the function declaration and application are merged into one. Similar to normal functions, the syntax for lambda functions includes its arguments and a function body that specifies how the result is calculated. However, instead of using a name for the function, we use the backslash symbol "\" (similar to the Greek letter lambda – λ), and instead of the equality symbol, we use the function arrow "->":

\<ARGUMENT1> <ARGUMENT2> -> <FUNCTION BODY>

We can directly use lambda functions just like any other function, so here is how we could use our triple function as a lambda function:

ghci> (\x -> x * 3) 4
12

Lambda functions are very useful for functions that are only used locally because we can simplify our code. For example, our previously defined function trackScore could be improved by using a lambda function to calculate the score:

trackScore4 :: Float -> Float -> String
trackScore4 time avgTime
  | time < avgTime = "Great! Your time is " ++ show (score) ++ " 
      seconds below average!"
  | time > avgTime = "Your time is " ++ show (score) ++ " seconds 
      above average."
  | otherwise = "Your time is on par with the average time!"
    where
      score = (\x y -> abs (x - y)) time avgTime