-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Let me offer a differing view of Monads. Monads are a way to write type-safe imperative programs within a functional framework. It's just an advanced version of PROGN kludge in LISP. Since they are based on a linear flow of "commands", they seem to necessitate sequential programming. Because of this reason I prefer not to use any monads whenever possible. It seems to eliminate the gist of functional programming. OTOH, the nice thing about Monads is that they, I think, lift the semantics of an imperative language, to the language level. When I look at the analysis of Algol-like languages in Tennent's "Semantics of Programming Languages" book I see the same thing as Monads: a way to sequence commands, and pipe the effects. Because of these reasons, I think the use of Monads are highly exaggerated. They are sort of like the over-use of "template" code in C++. In my experience, it doesn't work too well. You will end up writing monadic versions of everything, etc. Of course, they are a nice way to abstact I/O. How else could you do it properly in a functional language? Monads effectively model the operation of a sequential machine (one I/O channel!) in a mathematical way. It's similar to the problem of trying to retrofit a parallel system in a sequential system. Consider a sequential input source, and a parallel algorithm to compute it. You will need an interface between the two. In that respect, whenever I use monads, I feel like going back to an imperative language because it will make my program much less concurrent. Wasn't the most important benefit of using a functional PL architecture independence? I think it has turned to "ease of programming" now, which isn't any more real. :) Thanks, On Wednesday 16 January 2002 17:05, you wrote:
I see a lot of literature that says that monads "simulate" the effects of imperative programming concepts.
I think that's just bad wording. To take a rather trite point of view, in a language such as C /everything/ is done within a monad, and all types, even int, are really IO something (IO Int).
In Haskell you may see costs associated with using Monads, but they are mainly to do with dealing with the difficulties that arise from having laziness everywhere.
Jón
- --
Eray Ozkural (exa)