Again, the high-level language is in charge, and it runs the legacy application as a subprocess. The legacy application needs no changes and can be written in any language, plus you're free to choose any GUI toolkit you find convenient. What makes that architecture different is its finer control over the subprocess. Perl and Tcl batch subprocesses with the backtick operator and the exec command, respectively. For concurrent operations, both languages use open .
Many languages can also open pipes.
Next month, we'll look at variations of the second architecture and introduce the third and final major architecture for combining legacy applications with scripted wrappers. In the news Important news about scripting languages breaks faster than we can write about it. Our particular congratulations, though, go to the Lua team for its recent release of version 4.0. This update is faster, improves error handling, is fully re-entrant, and includes several other important advances. Cameron Laird and Kathryn Soraiz manage Phaseit, a software consultancy just outside Houston.