Question: Print nothing when using a procedure

**I am trying write a procedure (bit(n,k)) that print all the binary sequences with 2 following conditions:
  - Each of the sequences has the length of 'n'. (n elements)
 - k bits of n elements have the value 1. (all the remains have the value 0)
   Example: bit(3,2) and the result is ((101),(110),(011)).
**My code:
bit := proc (n, k)
     local one, index, i, d;
     global A;
     one := 0;
     index := 1;
     A := [seq(0, i = 1 .. n)];
     d := proc (index)
        if one = k or index = n+1 then return NULL; end if;
        for i from 0 to 1 do
              A[index] := i;
              if i = 1 then one := one+1; end if;
              if one = k then print(op(A)); end if;
             if i = 1 then one := one-1; A[index] := 0; end if;
        end do;
     end proc;
end proc;
0, 0, 0, 0, 1
That 's not the answer for the excercise. What is the problem?


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