Debugging Standard ML
Report ID: TR-378-92Author: Tolmach, Andrew P.
Date: 1992-10-00
Pages: 219
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Abstract:
Traditional ''source--level'' debuggers for compiled languages actually operate at machine level, which makes them complex, difficult to port, and intolerant of compiler optimization. For type--safe languages, however, debugging support can be provided without reference to the underlying machine, by adding instrumentation to program source code before compilation. Because the instrumented code is (almost) ordinary source, it can be processed by the ordinary compiler. The debugger is thus independent from the underlying hardware and runtime systems, and from the optimization strategies used by the compiler. This dissertation describes the design and implementation of instrumentation--based debuggers for the Standard ML of New Jersey compiler. Three systems are described: a simple debugger with ordinary variable display and breakpoint facilities, a debugger supporting --- and taking advantage of --- reverse execution, and a debugger for ML Threads, a concurrent extension of ML running on multiprocessors. A formal operational semantics for a subset of ML is used to define debugging operations precisely, and to provide a basis for determining the concrete types of polymorphic variables at runtime. Debugger performance measurements are presented for a range of real programs.