Loop: remove the characters at the beginning

Help!
1

Hello.

loop_entry(A,[Head|List],X) :-
  print(List),
Head == A,
  loop_entry(A,[List],X).

?- loop_entry(a,[a,a,a,a,b,c,d,e,f],X).

I get the result:

[a,a,a,b,c,d,e,f][]
false.

But I want the result:

b,c,d,e,f

I want to delete all a’s at the beginning of the list.
I think : Head == A,
is the problem.

Does not work, too:

loop_entry(A,[H|L],V) :-
   L \== A.

loop_entry(A,[Head|List],X) :-
  print(List),
  loop_entry(A,[List],X).

L == A. For some reason He cannot compare characters?

Thanks

2

| PrologAxel
October 23 |

  • | - |

Hello.

`

loop_entry(A,[Head|List],X) :-

  print(List),

Head == A,

  loop_entry(A,[List],X).

`

?- loop_entry(a,[a,a,a,a,b,c,d,e,f],X).

I get the result:
[a,a,a,b,c,d,e,f]
false.

But I want the result:
b,c,d,e,f

I want to delete all a’s at the beginning of the list.
I think : Head == A,
is the problem.

Does not work, too:

loop_entry(A,[H|L],V) :-
L == A.

loop_entry(A,[Head|List],X) :-
print(List),
loop_entry(A,[List],X).

L == A. For some reason He cannot compare characters?

This should be “Head = A”, not “Head == A”.

Cheers
Volker

1 Like
3

The following seems what you have in mind. If so, I’m happy.

% ?- loop_entry(a, [a,a,a,b,c], X).
%@ X = [b, c].
% ?- loop_entry(a, [b,c], X).
%@ X = [b, c].

loop_entry(A, [ A | List ], X) :-!, loop_entry(A, List, X).
loop_entry(_, List, List).

K.M.

1 Like
4

Thank you. This was exactly what I was looking for.