Dear friends of the most advanced Standard ML system on the planet.
Some month ago, David Matthews has reworked the internal interface for source-level debugging, see also http://www.polyml.org/documentation/Reference/PolyMLDebuggerInterface.html (This requires an intermediate repository version of Poly/ML, until a proper release emerges.)
I've already wrapped up the debugger in the Prover IDE framework of Isabelle. A fully integrated version can be downloaded for testing here: http://www4.in.tum.de/~wenzelm/test/Isabelle_20-Aug-2015 and a minal example here: http://www4.in.tum.de/~wenzelm/test/Isabelle_20-Aug-2015/Debugger_Example.th...
The Debugger panel can be opened via the Isabelle/jEdit menu "Plugins / Isabelle / Debugger panel" or the jEdit action "isabelle-debugger". Without such a panel, there is no effect on the running ML program.
What is also interesting in this preview of the next Poly/ML release is native support for x86-windows, based on MingW32 instead of Cygwin. Cygwin remains the portable system glue for the Isabelle environment, but both the IDE front-end (Scala/JVM) and the ML backend are now fully at home on Windows.
Makarius