[Haskell-cafe] What is <-
lemming at henning-thielemann.de
Sun Aug 8 11:36:16 EDT 2010
On Sun, 8 Aug 2010, michael rice wrote:
> That was my suspicion. So, you can't change horses (monads) in mid-stream.
> A parallel question:
> main = do ... -- in the IO monad
> I know I can have other *do*s in main,
> if foo
> then do
> else do
> but must all these other *do*s also be in the same IO monad? What determines what monad
> a *do* is "in"? The first line after the *do*?
'do' is just syntactic sugar that is expanded to '>>=' and '>>'
combinators. Determining the monad is the task of type inference. Since x,
y and (if b then x else y) must have the same type, so if they are monadic
actions, they are all of the same monad type.
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