Introduction to MrSpidey

MrSpidey is an interactive, static debugger for Scheme designed to help programmers understand and debug complex programs. It automatically infers information about the run-time behavior of programs, and uses this information to identify potential ``danger-points'' in those programs. Specifically, MrSpidey:

• infers a type, or value set invariant, describing the set of possible values for each program expression;
• uses this information to identify unsafe program operations that may cause run-time errors; and
• provides a supporting graphical explanation for these invariants.

MrSpidey supports almost all of DrScheme, which is an extension of R4RS Scheme with structures, a module system, an object system, and a GUI toolbox. For further information on the technology underlying MrSpidey, see [1, 3, 4, 5, 2].

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