I believe it's in there, no? (Requires the java 7 runtime, if memory serves?)

Can you link to an example or something?

Here's the example from Mirah's repo: https://github.com/mirah/mirah/blob/master/examples/dynamic....

It does require Java 7 and there's no plans to make it work on Java 6-. Unlike the rest of Mirah, this feature (if you use it) does require a runtime library, since Java 7 / invokedynamic do not ship anything builtin for choosing a target Java method. We use Attila Szgedi's "dynalink" project, which provides a default dynamic linker based on Java language specification method selection rules.

Long story short: yes, Mirah can support dynamic dispatch as well, but it needs a little bit of runtime library to support that.