makePrismsの再実装はつらみしか無さそうなので、実際のLensで動きだけ確認

gistfile1.hs

{-# LANGUAGE TemplateHaskell #-}
module Main where
import Control.Lens

data Foo a b = Hoge a | Piyo b | Fuga String 
  deriving (Show, Read, Eq, Ord)

makePrisms ''Foo

-----

foo1 :: Foo Int Bool 
foo1 = Hoge 10

foo2 :: Foo Int Bool 
foo2 = Piyo True

foo3 :: Foo Int Bool 
foo3 = Fuga "Hello"

foo4 :: Foo (Int, Bool, String) Bool 
foo4 = Hoge (10, False, "Hoge")

main :: IO ()
main = do
  let foos = (foo1, foo2, foo3, foo4)
  print foos
  putStrLn "----------"
  print $ foos^?_3._Fuga
  print $ foos^?_4._Piyo
  print $ foos^?_4._Hoge._1
  putStrLn "----------"
  print $ foos&_2._Piyo.~False
  print $ foos&_4._Hoge._3.~"Hello! Prism"