Question

目前我可以生成表达式树。

expression_tree([_|N_s],N_s, [number(0)]).
expression_tree([_|N_s0],N_s1, [op(neg),[E1]]) :-
    expression_tree(N_s0,N_s1, E1).
expression_tree([_|N_s0],N_s2, [op(add), [E1, E2]]) :-
    expression_tree(N_s0,N_s1, E1),
    expression_tree(N_s1,N_s2, E2).

generate_expression(N_c, E) :-
    length(N, N_c),
    expression_tree(N,[], E).

?- generate_expression(N,E).
N = 1,
E = [number(0)] ;
N = 2,
E = [op(neg), [[number(0)]]] ;
N = 3,
E = [op(neg), [[op(neg), [[number(0)]]]]] ;
N = 3,
E = [op(add), [[number(0)], [number(0)]]] ;
N = 4,
E = [op(neg), [[op(neg), [[op(neg), [[number(0)]]]]]]] ;
N = 4,
E = [op(neg), [[op(add), [[number(0)], [number(0)]]]]] ;
N = 4,
E = [op(add), [[number(0)], [op(neg), [[number(0)]]]]] ;
N = 4,
E = [op(add), [[op(neg), [[number(0)]]], [number(0)]]] ;
N = 5,
E = [op(neg), [[op(neg), [[op(neg), [[op(neg), [[number(0)]]]]]]]]]

其中N是树的节点数。

我也可以独立生成序列号。

sequence_number(Sequence_number) :-
    sequence_numbers(1, Sequence_number).

sequence_numbers(I, I).
sequence_numbers(I, K) :-
    J is I + 1,
    sequence_numbers(J, K).

?- sequence_number(N).
N = 1 ;
N = 2 ;
N = 3 ;
N = 4 ;
N = 5 ;
N = 6

我也可以生成并输出表达式，但不能输入正确的序列号

print_expression(Stream, Prefix, Suffix, Sequence_number, E) :-
    write(Stream,Prefix),
    format(Stream, '~|~`0t~d~7+', Sequence_number),
    write(Stream,", "),
    write(Stream,E),
    write(Stream,Suffix),
    nl(Stream).

print_expressions_a(Stream, Prefix, Suffix, Sequence_number, N) :-
    generate_expression(N, E),
    print_expression(Stream, Prefix, Suffix, Sequence_number, E).

print_expressions_a :-
    Stream = user_output,
    Prefix = '(',
    Suffix = ')',
    Sequence_number = 1,
    N = 4,
    print_expressions_a(Stream, Prefix, Suffix, Sequence_number, N).

?- print_expressions_a.
(0000001, [op(neg),[[op(neg),[[op(neg),[[number(0)]]]]]]])
true ;
(0000001, [op(neg),[[op(add),[[number(0)],[number(0)]]]]])
true ;
(0000001, [op(add),[[number(0)],[op(neg),[[number(0)]]]]])
true ;
(0000001, [op(add),[[op(neg),[[number(0)]]],[number(0)]]])
true ;
false.

请注意，序列号均为0000001。

哪个生成选择点，所以我使用forall

对其进行了修改

print_expressions_b(Stream, Prefix, Suffix, Sequence_number, N) :-
    forall(
        generate_expression(N, E),
        print_expression(Stream, Prefix, Suffix, Sequence_number, E)
    ).

print_expressions_b :-
    Stream = user_output,
    Prefix = '(',
    Suffix = ')',
    Sequence_number = 1,
    N = 4,
    print_expressions_b(Stream, Prefix, Suffix, Sequence_number, N).

?- print_expressions_b.
(0000001, [op(neg),[[op(neg),[[op(neg),[[number(0)]]]]]]])
(0000001, [op(neg),[[op(add),[[number(0)],[number(0)]]]]])
(0000001, [op(add),[[number(0)],[op(neg),[[number(0)]]]]])
(0000001, [op(add),[[op(neg),[[number(0)]]],[number(0)]]])
true.

这仍然是错误的。

我寻求的输出是

(0000001, [op(neg),[[op(neg),[[op(neg),[[number(0)]]]]]]])
(0000002, [op(neg),[[op(add),[[number(0)],[number(0)]]]]])
(0000003, [op(add),[[number(0)],[op(neg),[[number(0)]]]]])
(0000004, [op(add),[[op(neg),[[number(0)]]],[number(0)]]])

每个序列号都是唯一的，并且从0或1开始顺序，并且可以写入文件。对于此示例，流设置为user_output以简化问题。

如果我将序列号生成器添加到混合

中

print_expressions_c(Stream, Prefix, Suffix, N) :-
    generate_expression(N, E),
    sequence_number(Sequence_number),
    print_expression(Stream, Prefix, Suffix, Sequence_number, E).

print_expressions_c :-
    Stream = user_output,
    Prefix = '(',
    Suffix = ')',
    N = 4,
    print_expressions_c(Stream, Prefix, Suffix, N).

?- print_expressions_c.
(0000001, [op(neg),[[op(neg),[[op(neg),[[number(0)]]]]]]])
true ;
(0000002, [op(neg),[[op(neg),[[op(neg),[[number(0)]]]]]]])
true ;
(0000003, [op(neg),[[op(neg),[[op(neg),[[number(0)]]]]]]])
true ;
(0000004, [op(neg),[[op(neg),[[op(neg),[[number(0)]]]]]]])
true ;
(0000005, [op(neg),[[op(neg),[[op(neg),[[number(0)]]]]]]])
true ;

序列号现在是正确的，但是从不生成新表达式，因为序列号生成器使用选择点来生成下一个序列号，因此谓词sequence_number不会回溯到{{1谓词来获得一个新的表达式。

那么，我可以使用两台依赖于回溯的发电机吗？如果是这样，怎么样？

补编

这与我之前关于树木生成器的问题有关我知道这应该用dcg完成，并且应该更改数据结构，但是当我试图理解这一点时，以这种方式看到它更容易理解。

相关SO问题

Answer 1

从一个纯粹务实的角度来看，一个计数器很容易实现（在SWI-Prolog中），具有不可回溯的分配：

print_expressions_d(Stream, Prefix, Suffix, N) :-
    generate_expression(N, E),
    inc(Sequence_number),
    print_expression(Stream, Prefix, Suffix, Sequence_number, E).

print_expressions_d :-
    Stream = user_output,
    Prefix = '(',
    Suffix = ')',
    N = 4,
    nb_setval(counter,1),
    print_expressions_d(Stream, Prefix, Suffix, N).

inc(V) :- nb_getval(counter,V), C is V+1, nb_setval(counter,C).

Answer 2

 def import_obj(self, instance, row, dry_run):
    super(RelationshipResource, self).import_obj(instance, row, dry_run)

    for field in self.get_fields():
        if isinstance(field.widget, widgets.ManyToManyWidget): 
            tags = []
            for tag in instance.tagtag.all():            
                    tags.append(tag.name)                        
            tags.extend(row['tagtag'].split(',')) # concat existing and new tagtag list
            row['tagtag'] = ', '.join(tags) #set as new import value
            # continue to save_m2m
            continue            
        self.import_field(field, instance, row)

梳理生成器结果并将结果写入流

补编

相关SO问题

2 个答案: