It recently came up on the Poly/ML mailing list that Isabelle/jEdit makes a pretty efficient SML IDE these days. I manage a fairly large SML project called Quantomatic, so I thought I'd have a go at getting a setup to work. I've got a setup now that I am pretty happy with, so I thought I'd share my results. Hopefully other people will find this helpful.
Quantomatic is fairly unique in that it is designed to run inside of Isabelle or as a standalone project. As a result, the whole codebase is implemented on top of an Isabelle/ML-like environment, obtained by importing chunks of the ML code in Pure. This can be done by copying src/Pure from Isabelle 2014 into an SML project and using this file:
https://github.com/Quantomatic/quantomatic/blob/integration/core/isabelle_en...
In the past, we used a slightly hacked-up version of Pure, but for the sake of maintainability, we now use an exact copy.
The project itself is loaded with special "thy" files that only contain comments and "ML_file" commands. These can be run from inside Isabelle/jEdit (in the "real" Isabelle/ML environment), or they can be imported in poly/ML with the function "use_thy":
https://github.com/Quantomatic/quantomatic/blob/integration/core/use_thy.ML
This implements a baby version of the outer syntax parser, which ignores imports and translates the ML_file commands into use statements. This makes the external ROOT.ML tiny and easy to maintain:
https://github.com/Quantomatic/quantomatic/blob/integration/core/ROOT.ML
This can be executed with, e.g. "poly --use ROOT.ML"