Yes, I had always desired that the operator >>= should have been right associative for this short cut even when written without the 'do' notation.
On Tue, May 13, 2008 at 3:39 AM, John Hamilton <[EMAIL PROTECTED]> wrote: > I'm trying to understand how short circuiting works with the Maybe monad. > Take the expression n >>= f >>= g >>= h, which can be written as > (((n >>= f) >>= g) >>= h) because >>= is left associative. If n is > Nothing, this implies that (n >>= f) is Nothing, and so on, each nested > sub-expression easily evaluating to Nothing, but without there being a > quick way to short circuit at the beginning. > > Now take the example > > do x <- xs > y <- ys > z <- zs > return (x, y, z) > > which I believe desugars like > > xs >>= (\x -> ys >>= (\y -> zs >>= (\z -> return (x, y, z)))) > > Here the associativity of >>= no longer matters, and if xs is Nothing the > whole expression can quickly be determined to be Nothing, because Nothing > >>= _ = Nothing. Am I looking at this correctly? > > - John > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >
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