Records (with optics?) #9
Description
Here's a records demo we wrote a while back:
import Numeric.Natural
data Person =
Person
{ name :: String -- ^ The person's given name
, age :: Natural -- ^ How many years old
}
deriving Show
main =
do
let a = Person { name = "Alice", age = 47 }
let b = Person { name = "Bob", age = 50 }
let c = b{ age = 51 }
putStrLn (show a)
putStrLn (show b)
putStrLn (show c)
putStrLn ("name: " ++ name c)
putStrLn ("age: " ++ show (age c))$ runhaskell records.hs
Person {name = "Alice", age = 47}
Person {name = "Bob", age = 50}
Person {name = "Bob", age = 51}
name: Bob
age: 51
Lately I'm feeling like the Phrasebook should just immediately introduce optics from the start.
{-# LANGUAGE TemplateHaskell #-}
import Numeric.Natural
import Optics
data Person =
Person
{ _name :: String -- ^ The person's given name
, _age :: Natural -- ^ How many years old
}
deriving Show
makeLenses ''Person
main =
do
let a = Person { _name = "Alice", _age = 47 }
let b = Person { _name = "Bob", _age = 50 }
let c = set age 51 b
putStrLn (show a)
putStrLn (show b)
putStrLn (show c)
putStrLn ("name: " ++ view name c)
putStrLn ("age: " ++ show (view age c))Maybe that's too radical. On the other hand, maybe introducing it now in an extremely simple context is good setup for a later page on doing "deep updates" with composed lenses. I think in a later page we could end up showing how to get a lot of of optics using only view, set, over, and (%) without being overwhelming.