On Fri, 2 Jan 2009, Achim Schneider wrote:
There are no lazy monads. Monads imply explicit sequencing... writing
I think this is an extremely bad thing to say and is a source of misunderstanding about monads and evaluation. Most monads _are_ lazy, and it is important to understand that when trying to understand the run-time properties of your monadic code. Monads sequence effects, but evaluation is an almost orthogonal issue. Here is a recent thread where I talk about laziness: http://www.reddit.com/r/haskell/comments/7itbi/mapm_mapm_and_monadic_stateme... (for the short short story, simply try out
take 10 $ execWriter (sequence_ (repeat (tell "x"))) )
Furthermore, the code in my article on recursive do from The.Monad.Reader issue #6 http://www.haskell.org/sitewiki/images/1/14/TMR-Issue6.pdf requires the monads to be lazy in order to tie the knot. -- Russell O'Connor http://r6.ca/ ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.''