Prolog -数字到单词

% 定义数字到单词的映射关系
number_word(0, zero).
number_word(1, one).
number_word(2, two).
number_word(3, three).
number_word(4, four).
number_word(5, five).
number_word(6, six).
number_word(7, seven).
number_word(8, eight).
number_word(9, nine).

% 定义递归规则，将数字转换为单词
number_to_word(0, [zero]).
number_to_word(Number, Words) :-
    Number > 0,
    Number < 10,
    number_word(Number, Word),
    Words = [Word].
number_to_word(Number, Words) :-
    Number >= 10,
    Number < 100,
    Ten is Number // 10,
    Unit is Number mod 10,
    number_word(Ten, TenWord),
    number_word(Unit, UnitWord),
    Words = [TenWord, UnitWord].

% 查询示例
?- number_to_word(42, Words).
Words = [four, two].