You don't normally call x::Int a computation of an Int because there's nothing that distinguishes the value of the x from what it was before you computed it. So I prefer to regard x as a value (in a domain, of course). But for x :: (Monad m) => m Int there is something else happening, so the word computation makes sense.
This is just the terminology people use, not an absolute truth, so you're free to think it's wrong. :)
BTW, if you regard non-termination as an effect then even x :: Int is a computation.
-- Lennart
On 8/14/07, Dan Piponi <dpiponi@gmail.com> wrote:
On 8/14/07, Jeff Polakow <jeff.polakow@db.com> wrote:
> One general intuition about monads is that they represent computations
> rather than simple (already computed) values:
> x :: Int -- x is an Int
> x :: Monad m => m Int -- x is a computation of an Int
What's a "computation"? It seems to me that in a lazy language, x::Int
represents a computation of an int, not an "already computed" value.
x::[Int] is a computation that returns multiple values. x::(Int,Int)
is a computation that returns a pair of values. x::() is a computation
that returns nothing. x::Map a b is a computation that gives a way to
associate values of type a with values of type b. Some of these are
monads, some are not. What's the difference between them? Why are you
calling certain values "computations"?
--
Dan
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