Io, Day 3: Thoughts
Although I'm only on the second language out of seven in the book, a pattern is emerging: day 1 is very basic syntax, day 2 is more advanced syntax, and day 3 shows you some of the advanced applications that set the current language apart from all the others.
It's a great strategy: each jump is small enough that you can follow along, but big enough that you're able to get a thorough look at the language in just a few days. In fact, my biggest complaint so far is that the examples in the final day of Io are very intriguing, but also very short, so I'm dying to see more.
In a single chapter, we tore through using metaprogramming and concurrency in the span of just a few pages. It was tough to appreciate it all in such a short time. I was able to get a little more practice with Io metaprogramming by implementing a super simple "doInTransaction" method similar to the one I created in Ruby:
The idea was to be able to run some code, such as starting and ending a transaction, before and after a "block" of statements. For added fun, I wanted to be able to support curly braces for defining blocks. Accomplishing both was trivial by taking advantage of the fact that Io treats "{" as the message "curlyBrackets". Handle that message properly in your object, add some basic introspection, and you're done.
Unfortunately, I wasn't able to think of a suitable "toy" example to learn more about coroutines. I'm still fuzzy on a lot of the nuances, such as how memory is shared between the "threads", how many threads there are, and how yield and resume really interact. I'd love to see some more examples, especially those that show a practical use case for Io actors.
Io, Day 3: Problems
Enhance Builder XML
Enhance the XML program (see the original source, the original test file, and the original output) to add spaces to show the indentation structure. Also, enhance the XML program to handle attributes: if the first argument is a map (use the curly brackets syntax), add attributes to the XML program. For example, book({"author": "Tate"}..) would print <book author="Tate">.
This is an awesome example of Io's flexibility and power when it comes to creating DSLs. In some 30 lines of code, Io can process this Builder format:
To produce the equivalent HTML output:
Most of the (surprisingly concise and elegant) builder source code came from the book. Here's my updated version that handles indentation and attributes:
The biggest stumbling point was trying to use addAssignOperator in the same file as the test script. This doesn't work: the OperatorTable has already been loaded and can't be changed. By splitting the code into two files, one for source and one for testing, I was able to properly handle the colon and avoid the very frustrating "Sequence does not respond to ':'" error.
Create a list syntax that uses brackets
A much easier problem, but another great example of the flexibility of Io: Ruby-like syntax for lists in just a couple lines of code.
Wrapping up Io
This was the last day of Io and I must admit, I'm a bit sad to see it go. It's a beautiful example of just how simple and flexible a language can be. Of course, being able - and tempted - to change just about anything is a bit of double-edged sword: more than once I saw unexpected consequences from overriding the "forward" method. However, it's undeniably powerful. If nothing else, Io has made me more excited to learn about the Lisp family, with Clojure being the 6th language in the book.
I wish I got to see some more examples of concurrency in Io, but the book was pretty sparse in that area. Even worse, I can't find much online. Unfortunately, Io's community is tiny. It's hard to justify spending too much time on a language that, in all honesty, I'll probably never use in any capacity besides learning.
Time for something new
Continue on to Prolog, Day 1, to learn about a radically different style of programming.
