What I don't understand is why a Perl editor should be written in Perl itself. You're ultimatly dealing with a stream of bytes, which is as a completly language-agnostic concept as you can find.

But woolfy was specifically describing a Perl-specific code editor, not an arbitrary-stream-of-bytes editor.

Beyond just syntax highlighting, such a tool might be expected to support the features of some advanced Java and Smalltalk code editors, like:

• symbol name lookup (tab-completion for variable names, when typing a function name show an example of the arguments it takes, etc);
• refactoring editor (for example, select a few lines of code and invoke the "move to new subroutine" refactoring, and automatically have those lines replaced by a call to a new subroutine with proper argument passing and return value assignment);
• run-time/debugger integration (interpreting code as you type, setting break points, editing code in a running program and then continuing);
• documentation support (WHYSIWYG POD editor, fill in some kinds of POD automatically);
• testing support (automatic running of tests in the background, integrated display of profiling results and code or pod coverage analysis);
• plugin support (to let others add support for working with Class::MethodMaker, Class::Contract, Aspect, or other specialized approaches to Perl coding).

Even if it only implemented some subset of the above, I think such an editor would be providing real value, beyond the traditional solution of a good text editor with syntax coloring and automatic indenting.

And I don't see how you could really do justice to such a tool without implementing it in Perl, or at least delegating key portions to an embedded Perl instance.