Julia has a rich and varied syntax, but it was always known that a vast wealth of code existed in object libraries covering a wide range of specialities. So, a simple mechanism to call functions from these libraries would prove to be useful, and a one-line native instruction call ccall() was added.
This has led to the development of packages that effectively wrap code around the existing application programming interfaces (APIs). An example would be to access a database that exposes an API to perform functions such as those to establish a database connection, to create and update records, and to execute queries.
Another major area of interoperability has been between Julia and Python, and we have already shown some evidence of that in using Python for displaying graphs and using the IPython system as a proxy IDE.
There is also some further work on interfacing with R, Java, and MATLAB, and I'll present a brief overview of this too later.
