In this presentation from the JVM Language Summit 2009, Allison Randal discusses what it means for a language to be dynamic, the spectrum between static and dynamic languages, dynamic typing, dynamic dispatch, introspection, dynamic compilation, dynamic loading, and a summary of the main differences between static and dynamic.
Different ways of looking at things can yield very different, complementary insights, for instance regarding light as waves or particles.
Most languages are actually centering on the middle of the range from very static to very dynamic.
CS has been focusing on the static perspective. (But Smalltalk has been extremely dynamic all along.)
Dynamic vs. static typing is really only about when type constraints are checked. Own note: that’s not completely true – e.g. compiler optimization. Also, later she mentions computing dynamic dispatch at compile time which is only possible with a strong (explicit) type systems.
Introspection is not necessarily dynamic, just more common in such systems. Information comes from different sources: asking the VM/interpreter, compile-time annotations, execute-time annotations (e.g. annotated stacktraces). Meta object models are essentially introspection information for your object systems, provided by making the classes first-class objects.
Dynamic compilation: lots of options such as eval, JIT, file-based etc. She mentions the REPL without naming it, calling it “interactive compilation” and giving Python as example – odd.
Dynamic loading is surprisingly varied, ranging from linking to name binding to mixins, traits and roles (which often mean the same thing).
Her conclusion is that we’ll have both dynamic and static systems for a long time to come and that’s a good thing. In the end it’s about tighter control vs greater abstraction and productivity vs performance.
There’s an interesting-looking paper on the Further Reading slide: “Static typing where possible, dynamic typing when needed: the end of the cold war between programming languages” by E. Meijer and P. Drayton.
Hey, it’s Ada Lovelace Day!
Today I get to kill two birds with one stone. It is Ada Lovelace Day, “an international day of blogging to draw attention to the achievements of women in technology and science. Seeing that I’m just about to publish notes on a talk by Allison, why not write a little about her. And there sure is a lot to write.
I became aware of Allison’s work when I got interested in the Perls, both 5 and 6. When I start something new, I like to dig deeply into the web community around it; it tells you something about the culture surrounding a product. If you do that for Perl, it’s impossible to miss Allison.
The blurb on her website says
Her first geek career was as a research linguist in eastern Africa. But eventually her love of coding seduced her away from natural languages to artificial ones. A C and dynamic language (Perl/Python/Ruby/etc) programmer by trade, Allison is the architect of Parrot, chairman of the Parrot Foundation, on the board of directors of The Perl Foundation, and founder and president of Onyx Neon Press. She also works for O’Reilly Media, planning the program for their Open Source Convention (OSCON).”
Naturally, for Perl people writing this up means repeating the obvious. But given the unfortunate perception of Perl these days, it’s worth showing that cool things are still happening in that community. Like Perl 6 and Parrot. A virtual machine that can run 30+ languages? Check.
Allison is one of the lead developers as well as a manager for both Perl 6 and Parrot. She also wrote the current version of the Artistic License that Perl uses. You can easily find lots of talks she’s been giving over the years at many conferences. So for Ada Lovelace day, thank you Allison for all your hard work for Perl!