Big expression in first argument - Haskell

What do you guys do when you have to pass a big expression to the first argument of a two argument function?

parse :: String -> Maybe Expr
parse str = (`runReaderT` []) $ do
  tokens <- lift $ tokenize str
  parseExpr tokens

The above is the "best" solution I have right now.

I usually use flip runReaderT [] do (with BlockArguments)

in the specific case there's this precedent in relude: https://hackage.haskell.org/package/relude-0.7.0.0/docs/Relude-Monad-Trans.html#v:usingReaderT

so you could probably get away with defining it yourself if you're going to use it often

if the second argument is very small especially, I prefer the flip option also (because it avoids parens)
I've also seen

runReaderT act []
where
  act = ...

if both arguments are not small I would probably bite the bullet and split on multiple lines (with some do abuse to avoid parens :sweat_smile: )

f
  do 3 + 5
  do 4 + 6