[mhd]

What makes a good UI language? The earlier patterns of GUI development (before the "reactive" hype train) were rather object-oriented, so having that helps (otherwise it quickly gets rather verbose, cf. Xt/gtk). And for smaller event handlers, anonymous functions/lambdas etc. Perl has that, but so do many other languages.

Speaking of verbosity, having to lay out all the widgets in an app with all their individual properties, coordinates etc. quickly gets quite dense. Here having things like good literal definitions, flexible arguments (variable/default) can make that a lot more concise.

If the language itself doesn't do that for you, tooling quickly becomes necessary. This can be a UI designer (which is usefule in any case), or some ad-hoc UI description language. Which tend to suck (UIL, XAML etc.), and thus require a UI builder application anyway.

Performance is sufficient. Perl always had a lot of packages to help integrating with services etc.

So, yeah, I'd say it's pretty decent, but hardly unique. That was true 20 years ago, and even more so now. Not that anyone cares about desktop UIs.