On 7/30/10 12:29, Tillmann Rendel wrote:
C K Kashyap wrote:
I am of the understanding that once you into a monad, you cant get out of it?
That's not correct.
There are many monads, including Maybe, [], IO, ... All of these monads provide operations (>>=), return and fail, and do notation implemented in terms of these functions, as a common interface. Using just this common interface, you cannot "get out of the monad".
But most if not all monads also provide additional operations, specific to the monad in question. Often, these operations can be used to "get out of that monad". For example, with Maybe, you can use pattern matching:
In fact, I would argue that a monad which you cannot escape from is not very useful at all. IO is the only exception I know of. Martijn.