I'm following Harper's blog, Existential Type¹, which I find to be an enjoyable and entertainingly written tirade about the advantages of teaching functional programming - specifically ML - to students. Of course, he tends to be critical of Haskell, but it's nice to get some thought provoking opinion from somebody who knows a bit about the business.
Recently, he had a piece on monads, and how to do them in ML, and one statement puzzled me:
"There is a particular reason why monads had to arise in Haskell, though, which is to defeat the scourge of laziness."
My own view is/was that monads were so successful in Haskell since it allowed writing flexible programs with imperative features, without sacrificing referential transparency. Although people are quick (and rightly so) to point out that this flexibility goes way beyond IO, I think IO was in many ways the killer application for monads. Before IO, we had very limited functionality (like 'interact' taking a 'String -> String' function and converting it into an exectuable program) to build real programs from.
Laziness does require referential transparency (or at least, it is easier to get away with the lack of RT in a strict language), so I can see that he is indirectly correct, but RT is a goal in itself. Thus, I wonder if there are any other rationale for a statement like that?
-k
¹ http://existentialtype.wordpress.com/ Interesting how I have been authoring and subsequently using monads in scala for several years and it is strictness that gets in the way more
On 02/05/11 17:54, Ketil Malde wrote: than anything. http://github.com/scalaz/scalaz/ I have been teaching functional programming for quite a while, both in universities and outside of academia, and I am of the opinion that Haskell's suitability in first place has no close second place. I wonder why I am wrong, but this post (and previous) is hardly persuasive. -- Tony Morris http://tmorris.net/