1. A method of generating an executable and user-modifiable trace file script, the method comprising: performing execution of an executable instruction stream that invokes a sequence of high-level procedures; and generating a trace file during execution of the executable instruction stream that represents invocations of the high-level procedure invocations as a human-readable script such that input parameters supplied to the high-level procedures by the executable instruction stream are documented in the trace file as immediate fixed values and such that return parameters supplied from the high-level procedures to the executable instruction stream are documented in the trace file as comments; and responsive to a subsequent command, performing execution of the trace file to reproduce at least part of the behavior of the executable instruction stream.