Internals of predicates that have been compiled without debug instructions cannot be traced by the debugger (only entering and leaving such a predicate can be shown). On the other hand, this code uses less space and runs slightly faster than code with debug instructions. So it makes sense to compile well-tested predicates without debug instructions. Note however that predicates with debug instructions that are called by predicates without debug instructions are also invisible to the debugger.
Calling nodbgcomp/0 is equivalent to set_flag(debug_compile, off), set_flag(variable_names, off).
Success: [eclipse]: nodbgcomp, [user], dbgcomp, [user]. q :- writeln(hi). user compiled 36 bytes in 0.00 seconds p :- q. user compiled 32 bytes in 0.00 seconds yes. [eclipse]: trace. Debugger switched on - creep mode yes. [eclipse]: p. (1) 0 CALL p (dbg)?- creep N (2) 1 CALL q (dbg)?- creep hi N (2) 1 EXIT q (dbg)?- creep % call to writeln/1 (1) 0 EXIT p (dbg)?- creep % invisible to the yes. % debugger.