使用分配给变量的列表时，b-prolog成员函数的行为可疑

Question

While interrogating b-prolog in the terminal, the member function does not seem to behave correctly when assigning a list to a variable and using the variable with the built in "member" function. I am having trouble interpreting the result when using a variable. Could anyone tell me if this is the correct behaviour and why it is the case?

B-Prolog Version 8.1, All rights reserved, (C) Afany Software 1994-2014.
| ?- List = [a,b,c,d].
List = [a,b,c,d]
yes
| ?- member(a,List).
List = [a|_14c] ?;
List = [_148,a|_154] ?;
List = [_148,_150,a|_15c] ?;
List = [_148,_150,_158,a|_164] ?;
List = [_148,_150,_158,_160,a|_16c] ?
yes

| ?- member(a,[a,b,c,d]).

yes
| ?-

I am using bprolog v 8.1 running on Windows 10 Pro (10.0.143393 Build 14393)

Answer 1

Top-level queries are independent and don't share variables. If you try instead:

| ?- List = [a,b,c,d], member(a,List).

you will get the expected results.