These functions existed in DeclareDesign 1.x but are not part of 2.0. Each compared two designs by printing their code, their draws, or their summaries side by side, which is a job for a diff of the two scripts. They error with a message saying so.
Usage
compare_designs(...)
compare_design_code(...)
compare_design_data(...)
compare_design_estimates(...)
compare_design_inquiries(...)
compare_design_summaries(...)
print_code(...)Details
compare_diagnoses(), which compares what two designs achieve rather than
how they are written, is implemented.