Applying a function to lists using applicative functors

applicativeDemo.hs

import Control.Applicative

-- Create a Person data type
data Person = Person {
    name     :: String,
    age      :: Int,
    language :: String
} deriving (Show)

-- Person is a data constructor, and has a function signature of
-- Person :: String -> Int -> String -> Person
-- On line 22, it is being put into an applicative context

-- `pure` is a function which puts a function into an Applicative context.
-- In this case, it being put inside the List context.
-- Then, the <*> function applies the function to each argument
-- in each list
cartesianProductOfPeople =
    let names = ["Alice", "Bob", "Carlos"] in
    let ages = [18, 25, 40] in
    let languages = ["English", "Spanish", "Portuguese"] in
    let applicativeMakePerson = pure Person in
    applicativeMakePerson <*> names <*> ages <*> languages

-- Print the cartesian product of people that we built in the previous function
main = mapM_ (putStrLn . show) cartesianProductOfPeople

-- Prints the following output
-- Person {name = "Alice", age = 18, language = "English"}
-- Person {name = "Alice", age = 18, language = "Spanish"}
-- Person {name = "Alice", age = 18, language = "Portuguese"}
-- Person {name = "Alice", age = 25, language = "English"}
-- Person {name = "Alice", age = 25, language = "Spanish"}
-- Person {name = "Alice", age = 25, language = "Portuguese"}
-- Person {name = "Alice", age = 40, language = "English"}
-- Person {name = "Alice", age = 40, language = "Spanish"}
-- Person {name = "Alice", age = 40, language = "Portuguese"}
-- Person {name = "Bob", age = 18, language = "English"}
-- Person {name = "Bob", age = 18, language = "Spanish"}
-- Person {name = "Bob", age = 18, language = "Portuguese"}
-- Person {name = "Bob", age = 25, language = "English"}
-- Person {name = "Bob", age = 25, language = "Spanish"}
-- Person {name = "Bob", age = 25, language = "Portuguese"}
-- Person {name = "Bob", age = 40, language = "English"}
-- Person {name = "Bob", age = 40, language = "Spanish"}
-- Person {name = "Bob", age = 40, language = "Portuguese"}
-- Person {name = "Carlos", age = 18, language = "English"}
-- Person {name = "Carlos", age = 18, language = "Spanish"}
-- Person {name = "Carlos", age = 18, language = "Portuguese"}
-- Person {name = "Carlos", age = 25, language = "English"}
-- Person {name = "Carlos", age = 25, language = "Spanish"}
-- Person {name = "Carlos", age = 25, language = "Portuguese"}
-- Person {name = "Carlos", age = 40, language = "English"}
-- Person {name = "Carlos", age = 40, language = "Spanish"}
-- Person {name = "Carlos", age = 40, language = "Portuguese"}