In the middle of another gold card, this one on Actors (PDF), a concurrent programming abstraction that Scala borrowed from Erlang. The Scala short tutorial on actors isn’t much help, at least not to someone who’s spent as little time with Scala as I have; mostly Mr. Haller just seems to show you the source code from the examples directory and say “see”? But I persevere.

In the course of said perseverance, I did run across one interesting link, which I post by way of bookmarking: Functional Java, “an open source library that aims to prepare the Java programming language for the inclusion of closures [and] serves as a platform for learning functional programming concepts by introducing these concepts using a familiar language.” Which sounds like exactly what Code Monkey needs.

So I gave my pizza lunch talk on monads today, having over the past couple of weeks snuck in considerably more than a single Gold Card day’s worth of work. I think it went fairly well and was mostly comprehensible, though on the comprehensibility front it probably helped that a lot of my statements were wrapped in “I’m not sure what…”, “I’m not sure whether…” and “I’m not sure why…” —

— which, if you think about it, is really just a kind of Option (a.k.a. Maybe), so it’s totally appropriate.

At least, that’s (provisionally) my story and I’m (for now) sticking to it.

I got as far (I think) as figuring out what a monad is (mostly), and (I think) how the Scala List and Option monads work (mostly), largely by porting (partially) List and Option to Java. I mean to turn the talk into a post here, but that’ll take a couple of days — maybe longer if I get ambitious about cleaning up the code examples.

What I didn’t get to in any detail was Dan’s question about state, which was sort of the main point of this investigation, along with I/O and error handling. Always leave yourself some work for tomorrow, I’ve been told….

I’m 3/4 of the way through my Gold Card day, and I think I can finally tell a monad from a modron, and even from a maenad. Whether this will translate into a presentation anyone else can understand is still an open question.

Meanwhile, I’ve discovered:

• A whole folder of monad examples in the Scala distribution.
• That trying to do higher-order functional programming in straight Java does, in fact, really blow. An example that takes 74 lines in Scala takes… well, I don’t really know how many lines it takes in straight Java, because nine classes and 195 lines in, I’m only up to line 37 in the original (single) Scala file. We could extrapolate and guess 390 lines, but I wouldn’t bet on it. Maybe those BGGA closures aren’t such a bad idea after all…
• James Iry’s “Monads are Elephants,” an introduction to Scala monads that’s got more words and less math than Burak Emir‘s. (Nothing against math — or Dr. Emir — but we language majors like our human-readable variable and function names.)
• “Scala for Java Refugees,” a nice tutorial from Daniel Spiewak.

And, last but not least:

• That “Introductions to monads are bit of cottage industry on the Internet.” (James Iry again.)

So much for my plan to get rich writing Monads for Dummies.