Question

Say I have the following custom data type and function in Haskell:

data Person = Person { first_name :: String, 
                       last_name :: String,
                       age :: Int 
                     } deriving (Eq, Ord, Show)

If I want to create a function print_age to print a Person’s age, like so: print_age (Person "John" "Smith" 21) , how would I write print_age to access the age parameter? I’m an Object Oriented guy, so I’m out of my element here. I’m basically looking for the equivalent of Person.age.

Answer 1

Function application is prefix, so age person would correspond to the person.age() common in OOP languages. The print_age function could be defined pointfree by function composition

print_age = print . age

or point-full

print_age person = print (age person)