Expressing do block using only monadic bind syntax

Question

As far as I know, do blocks in Haskell are just some kind of syntactic sugar for monadic bind operators. For example, one could convert

main = do f <- readFile "foo.txt"
          print f
          print "Finished"

to

main = readFile "foo.txt" >>= print >> print "Finished"

Can all do blocks be converted to bind syntax? What about, for example, this block where f is used multiple times:

main = do f <- readFile "foo.txt"
          print $ "prefix " ++ f
          print $ f ++ " postfix"

Assuming we are in the IO monad, it is not possible to simply execute the readFile computation twice. How can this example (if possible at all) expressed using only bind syntax?

I think using Control.Monad is no solution, because it internally uses do blocks.

I think it it's possible to express this using arrows (using &&&) -- maybe this is a case where only arrows can be used as a generalization of monads?

Note that this question is not about the special examples above but about the general case of the result of a computation being used multiple times in monadic expressions like print.

Answer 1

Yes, all of them can be converted to bind syntax; in fact, they are converted internally by the compiler.

I hope this translation of your example gives you the hint:

main = readFile "foo.txt" >>= \f ->
       (print $ "prefix " ++ f) >>
       (print $ f ++ " postfix")