Re: [Haskell-cafe] Explaining monads

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 wrote:

On 8/14/07, Jeff Polakow wrote:

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One general intuition about monads is that they represent computations rather than simple (already computed) values:

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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 _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe