I have this tracing meta interpreter, altered from previous question Prolog unbind bound variable.
I don't understand how to interpret cut. Thanks to user @false who told me that the cut is badly implemented, my question is, how should I implement cut in this meta-interpreter?
%tracer
mi_trace(Goal):-
mi_trace(Goal, 0).
mi_trace(V, _):-
var(V), !, throw(error(instantiation_error, _)).
mi_trace(true, _Depth):-!, true.
mi_trace(fail, _Depth):-!, fail.
mi_trace(A > B, _Depth):-!, A > B.
mi_trace(A < B, _Depth):-!, A < B.
mi_trace(A =< B, _Depth):-!, A =< B.
mi_trace(A >= B, _Depth):-!, A >= B.
mi_trace(A = B, _Depth):-!, A = B.
mi_trace(A is B, _Depth):-!, A is B.
mi_trace(\+A, _Depth):-!, \+mi_trace(A, _Depth).
mi_trace(!, _Depth):-!, fail. % <- this is wrong
mi_trace((Goal1, Goal2), Depth):-
!,
mi_trace(Goal1, Depth),
mi_trace(Goal2, Depth).
mi_trace(Goal, Depth):-
display('Call: ', Goal, Depth),
redo_clause(Depth, Goal, Body),
Depth1 is Depth + 1,
mi_trace(Body, Depth1),
display('Exit: ', Goal, Depth).
mi_trace(Goal, Depth):-
display('Fail: ', Goal, Depth),
fail.
redo_clause(Depth, Goal, Body) :-
findall(Goal-Body, clause(Goal, Body), [First|Rest]),
( Goal-Body = First
; length(Rest, RL), length(RestC, RL),
member(Goal-Body,RestC),
display('Redo: ', Goal, Depth),
Rest = RestC
).
display(Message, Goal, Depth):-
tab(Depth), write(Depth), write(': '), write(Message),
write(Goal), nl.
trace_query(In, Out, Query):-
consult(In),
tell(Out),
call_with_depth_limit(findall(Query, mi_trace(Query), _Solutions), 30, _XMessage),
writeln(_XMessage),
writeln(_Solutions),
told,
unload_file(In),
true.