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_statements/c06s6pm
(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.''
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