如何在序言中加入规则并打印输出 [英] How to join rules and print out outputs in prolog

问题描述

我有以下事实清单.

items(itemId('P01'),prodName('Pots'),stockQty(50),price(8200)).
items(itemId('P02'),prodName('Pans'),stockQty(50),price(400)).
items(itemId('P03'),prodName('Spoons'),stockQty(50),price(200)).
items(itemId('P04'),prodName('Forks'),stockQty(50),price(120)).
items(itemId('P05'),prodName('Kettles'),stockQty(50),price(500)).
items(itemId('P06'),prodName('Plates'),stockQty(50),price(60)).

当给出像 print_all_products. 这样的命令时，如何在控制台上打印如下内容.

How to print on the console something like the following when a command like print_all_products. is given.

................

..............

可用产品

.........

名称数量

锅 60

平底锅 50

勺子 40

.................

..................

• 名称和数量必须以表格结构正确格式化.

我尝试使用 forall 和 foreach 我没有成功生成我需要的东西.

I tried using forall and foreach I am unsuccessful in generating what i need.

推荐答案

更多细节的答案已发布 此处.以下是代码，因此这不仅仅是链接答案.

Answer with more details is posted here. Below is the code so that this is not a link only answer.

items(itemId('P01'),prodName('Pots'),stockOty(50),price(8200)).
items(itemId('P02'),prodName('Pans'),stockOty(50),price(400)).
items(itemId('P03'),prodName('Spoons'),stockOty(50),price(200)).
items(itemId('P04'),prodName('Forks'),stockOty(50),price(120)).
items(itemId('P05'),prodName('Kettles'),stockOty(50),price(500)).
items(itemId('P06'),prodName('Plates'),stockOty(50),price(60)).

header("\n........................\nAvailable Products\n........................\nName   Qty\n").
footer("........................\n").

spaces(Length,Spaces) :-
    length(List,Length),
    maplist([_,0'\s]>>true,List,Codes),
    string_codes(Spaces,Codes).

padded_string(String,Width,Padded_string) :-
    string_length(String,String_length),
    Padding_length is Width - String_length,
    spaces(Padding_length,Padding),
    atom_concat(String,Padding,Padded_string).

format_detail_line(item(Name,Quantity),width(Name_width),Formatted_item) :-
    padded_string(Name,Name_width,Padded_name),
    atom_concat(Padded_name,Quantity,Formatted_item).

add_detail_line(width(Name_Width),Item,Lines0,Lines) :-
    format_detail_line(Item,width(Name_Width),Formatted_item),
    atomic_list_concat([Lines0,Formatted_item,"\n"], Lines).

items_detail(Detail) :-
    findall(item(Name,Quantity),items(_,prodName(Name),stockOty(Quantity),_),Items),
    aggregate_all(max(Width),Width,(items(_,prodName(Name),_,_),string_length(Name,Width)),Name_Width),
    Name_field_width is Name_Width + 1,
    foldl(add_detail_line(width(Name_field_width)),Items,"",Detail).

print_all_products(Report) :-
    header(Header),
    items_detail(Detail),
    footer(Footer),
    atomic_list_concat([Header,Detail,Footer], Report).

print_all_products :-
    print_all_products(Report),
    write(Report).

:- begin_tests(formatted_report).

test(1) :-
    print_all_products(Report),
    with_output_to(atom(Atom),write(Report)),
    assertion( Atom == '\n........................\nAvailable Products\n........................\nName   Qty\nPots    50\nPans    50\nSpoons  50\nForks   50\nKettles 50\nPlates  50\n........................\n' ).

:- end_tests(formatted_report).

---

注意:Peter 给出的 answer 是进行格式化的惯用方式，但正如我所指出的，这会驱动我疯了.即便如此，这也是我在生产环境中的做法.

---

Note: The answer given by Peter is the customary way to do the formatting, but as I noted, that drives me nuts. Even so, that is the way I would do it in a production environment.

我给出这个答案是因为 OP 指出他们正在寻找一种使用诸如 forall/2 或 foreach/2 之类的谓词来做到这一点的方法.当然，本答案中未使用它们中的任何一个，但使用了使用更实用的方法的意图.

I gave this answer because the OP noted they were looking for a way to do it using predicates like forall/2 or foreach/2. Granted neither of them is used in this answer but the intent of using a more functional approach is used.

如果问题更开放，我会使用 DCG 给出答案.

If the question was more open ended I would have given a answer using DCGs.

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