nonoverlapping_patterns.hs

{-# OPTIONS_GHC -Wall #-}
{-# LANGUAGE TemplateHaskell #-}

import Control.Lens
import Data.Bool

data DataTypeWithMillionsOfConstructors =
  DataTypeWithMillionsOfConstructors0
  | DataTypeWithMillionsOfConstructors1
  | DataTypeWithMillionsOfConstructors2
  | DataTypeWithMillionsOfConstructors3
  | DataTypeWithMillionsOfConstructors4
  | DataTypeWithMillionsOfConstructors5
  | DataTypeWithMillionsOfConstructors6
  | DataTypeWithMillionsOfConstructors7
  | DataTypeWithMillionsOfConstructors8
  | DataTypeWithMillionsOfConstructors9
  deriving (Eq, Ord, Show)

boolyFunction :: DataTypeWithMillionsOfConstructors -> String
boolyFunction DataTypeWithMillionsOfConstructors0 = "abc"
-- it would really suck to have to write out all the constructors
-- to achieve non-overlapping patterns
-- At some point we must trade off -- with this trade, I agree.
boolyFunction msg = show msg ++ "def"

----

-- but really, you want optics anyway

-- make all the prisms
makeClassyPrisms ''DataTypeWithMillionsOfConstructors

boolyFunction' :: DataTypeWithMillionsOfConstructors -> String
-- boolyFunction' = \x -> bool "abc" (show x ++ "def") (isn't _DataTypeWithMillionsOfConstructors0 x)
boolyFunction' = bool "abc" . (++ "def") . show <*> isn't _DataTypeWithMillionsOfConstructors0

-- demonstrate the type of _DataTypeWithMillionsOfConstructors0
typeof :: AsDataTypeWithMillionsOfConstructors x => Prism' x ()
typeof = _DataTypeWithMillionsOfConstructors0

boolyFunction' = bool "abc" . (++ "def") . show <*> isn't _DataTypeWithMillionsOfConstructors0 is neat