Prolog：嵌套列表

Question

我有这个Prolog代码：

pick_number_simple([],[]).
pick_number_simple([H|T],[H|T2]):- 
    number(H), pick_number_simple(T,T2).
pick_number_simple([H|T],T2):-
    not(number(H)), pick_number_simple(T,T2).

从列表中获取数字。例如：

pick_number_simple([d,f,7,5,e,3,g], NumList)

给你：

[7,5,3]

但我想让它从嵌套列表中获取数字。

例如：

pick_numbers_general([a,b,1,[2,[c,3]],d],1,NumList)

会给你：

[2,3]

我该怎么做？

Answer 1

你可以使用flatten/2 predicate

pick_number_simple([],[]).
pick_number_simple([H|T],[H|T2]):- 
    number(H), pick_number_simple(T,T2).
pick_number_simple([H|T],T2):-
    not(number(H)), pick_number_simple(T,T2).

pick_numbers_general(List, Num, NumList) :-
    flatten(List, NestList),
    pick_number_simple(NestList, NumListAll),
    findall(X, (member(X, NumListAll),X > Num), NumList).

所以

?- pick_numbers_general([a,b,1,[2,[c,3]],d],1,NumList).
NumList = [2, 3] ;