Equivalent of Haskell do-notation or F# Computation Expressions in Scala?

F# Computation Expressions allow to hide the complexity of monadic syntax behind a thick layer of syntactic sugar. Is there something similar available in Scala?

I think it's for comprehensions ...

Example:

val f = for {
  a <- Future(10 / 2) // 10 / 2 = 5
  b <- Future(a + 1)  //  5 + 1 = 6
  c <- Future(a - 1)  //  5 - 1 = 4
 } yield b * c         //  6 * 4 = 24

 val result = f.get

But it doesn't really feel right. Is there a better syntax?

for exemple in haskell you would have

    main = do fromHandle <- getAndOpenFile "Copy from: " ReadMode
          toHandle   <- getAndOpenFile "Copy to: " WriteMode 
          contents   <- hGetContents fromHandle
          hPutStr toHandle contents
          hClose toHandle
          putStr "Done."

this u开发者_StackOverflow社区nlike scala doesn't look like a foreach loops. Scala syntax seem to have too strong coupling with List comprehension which is a distinct concept. Which prevent me from writing internal DSL (monad) that doesn't look strange.

The missing piece is probably the use of = is scala's for-comprehensions:

val f = for {
  a <- Future(10 / 2) // 10 / 2 = 5
  b <- Future(a + 1)  //  5 + 1 = 6
  c <- Future(a - 1)  //  5 - 1 = 4
  d = b * c           //  6 * 4 = 24
} yield d


val result = f.get

With judicious mixing of both <- and =, you should have all the flexibility you need.

It seem like there is no such syntax available in scala and we would need to implement it ourself using the compiler plugin architecture.