DREAM IN CODE

let’s first take a look at some list functions, and see what’s the characteristic they all share sum : computes the sum of the numbers of a structure; and : returns the conjunction of a container of Bools; map : map f xs is the list obtained by applying f to each element of xs . There three are all common list function, and act very differently, but can be defined recursively using pattern matching as follow: mySum :: ( Num t) => [t] -> t mySum [] = 0 -- sum of empty is 0 mySum (x : xs) = x + mySum xs -- otherwise, add first element to sum of rest of the list myAnd :: [ Bool ] -> Bool myAnd [] = True -- and of empty is True myAnd (x : xs) = x && myAnd xs -- otherwise, return the conjunction of first element and the rest of list myMap :: (t -> t) -> [t] -> [t] myMap _ [] = [] -- map any function to empty is empty myMap f (x : xs) = f x : myMap f xs -- otherwise, prepend