I played around with JEdit a bit last night, and liked what I saw. It's fast, the documentation is helpful, and it was pretty easy to get started writing a syntax highlighting mode for Nice. I'm not sure I'm going to be able to use the builtin parsing options to actually do the highlighting of types and type constraints the way I'd ideally like to, but it looks pretty good already. To install, just save the file at the link above to your JEdit modes folder, and add these lines to your "catalog" file in the same folder:

<MODE NAME="nice"		FILE="nice.xml"

				FILE_NAME_GLOB="*.nice" />

I supposed I'll need to talk to the JEdit people now about getting it into the standard distribution.