Tuilib is a mess. Output occurs both in wrappers and parse_input, freeing may occur in wrapper, may in parse_input. Working with it is confusing. My thoughts:

• parse_input does not read anything from callbacks, hence callback return type is void, not void*
• All of the output occurs in callback.
• Sanity checks occur in callback, not in the inner function.
• Inner functions can only fail due to some codebase issue, not runtime issue. That means that inner function fail leads to termination of the program.
• All runtime errors of inner functions (key not found, no space left in the table) should propagate back to callback and all of the logic takes place there.