Some record types

gistfile1.hs

data Foo = Foo { a :: Int, b :: Int }
data Bar = Bar { x :: Foo, y :: Foo }

gistfile2.hs

one = modify $ \bar -> bar { x = (x bar) { a = 1 } }

gistfile3.hs

one = putf (x // a) 1

gistfile4.hs

one = modify $ \foo -> foo { a = 1 }
one' = modify $ \bar -> bar { x = execState one $ x bar, y = execState one $ y bar }

gistfile5.hs

one = putf a 1
one' = enter x one >> enter y one

gistfile6.hs

one' = modify $ \bar -> bar { x = x { a = 1 }, y = y { a = 1 } }