On Oct 26, 2012, at 11:06 AM, Brian Craft wrote: > I've read about four tutorials on monads so far, but it still escapes me. > > In fact, I'm still not sure what problem it solves.
Monads are hard to understand, and I too found I wasn't the target audience for the explanations I read. I finally had to write my own as a way to force me to understand. Advertisement: the explanation is in chapter 10 and the optional chapters 15 and 16 of my book. (URL in my signature.) People seem to like mine because I start with the implementation, not the abstract ideas. Also, I lie when necessary on the way to the complete explanation. The problem monads solve is twofold: 1. Suppose you have a series of computational steps. The results of those steps have to be combined in some way. A monad lets you move the combination rules away from the steps, so that you don't have to look at them. You just look at the steps and keep the rules in the back of your mind. That reduces code clutter. 2. Often, the rules are more general purpose than the steps. For example, it's common to want to break out of a series of steps when an error happens. Rather than scattering `if`s between some steps, you can point the Error monad at them. (When is that better than just using try/catch? -- that's still an open question to me.) That said, the *really* general-purpose monads tend to get written into the language as special forms. Clojure's `let` and `for` are both monads, but you don't need to know that to use them. One thing that's important to realize about monads is that they apply the *same* rule to every step. That seems to make them clunky when you're working on problems that aren't nicely structured. But for certain structured problems, especially ones that lend themselves to combinations of predefined rules that apply to every step, monads are just The Right Thing. Even if you don't use them, I'm inclined to think monads are a useful example of how to think about functions in a functional language. It helps you avoid just writing C code in Clojure. ----- Brian Marick, Artisanal Labrador Contract programming in Ruby and Clojure Occasional consulting on Agile Writing /Functional Programming for the Object-Oriented Programmer/: https://leanpub.com/fp-oo -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
