问题描述
我有一个像 'id1,id2,id3' 这样的原子，我想把它分成列表与 SWI 中的谓词 atomic_list_concat/3 相同.
i have an atom like 'id1,id2,id3' and i want to split it into list with same way as the predicate atomic_list_concat/3 in SWI .
预期结果
?- atomic_list_concat(L, ',', 'id1,id2,id3').
L = [id1, id2,id3]
?- atomic_list_concat([id1,id2,id3], ',', A).
A = 'id1,id2,id3'
无论如何，是否可以使用DCG
anyway, is it possible to do it using DCG
推荐答案
不考虑效率，这看起来很相似
without any regard to efficiency, this seems fairly similar
atomic_list_concat_(L, Sep, Atom) :-
( atom(Sep), ground(L), is_list(L) )
-> list_atom(L, Sep, Atom)
; ( atom(Sep), atom(Atom) )
-> atom_list(Atom, Sep, L)
; instantiation_error(atomic_list_concat_(L, Sep, Atom))
.
list_atom([Word], _Sep, Word).
list_atom([Word|L], Sep, Atom) :-
list_atom(L, Sep, Right),
atom_concat(Sep, Right, Right1),
atom_concat(Word, Right1, Atom).
atom_list(Atom, Sep, [Word|L]) :-
sub_atom(Atom, X,N,_, Sep),
sub_atom(Atom, 0,X,_, Word),
Z is X+N,
sub_atom(Atom, Z,_,0, Rest),
!, atom_list(Rest, Sep, L).
atom_list(Atom, _Sep, [Atom]).
基本原理
atomic_list_concat/3 是 SWI-Prolog 中内置的一个便利，我认为我的代码没有完全涵盖规范(主要是因为我缺少 SICStus Prolog 进行测试).一个值得注意的区别是可接受类型的限定.对于列表元素，我坚持使用 atom 而不是 atomic 类型，因为 atom_concat/3 它是 ISO 内置的，因此应该禁止 SWI 接受的某些模式-Prolog 实现.
atomic_list_concat/3 is a convenience built-in in SWI-Prolog, I think my code doesn't cover fully the specification (mainly because I lack SICStus Prolog for testing). A noteworthy difference is the qualification of acceptable types. I'm sticking to atom instead of atomic types for list' elements, because atom_concat/3 it's an ISO built-in, as such should ban some patterns accepted by SWI-Prolog implementation.
关于代码，当类型测试决定了转换的方向时，实现很简单:我在 list_atom/3 中选择了一个简单的递归连接，它可以很容易地优化，例如添加一个累加器，从而使它尾递归优化，而atom_list/3从左到右扫描寻找分隔符，找到后存入list head，得到正确的部分进行递归.
About the code, when the type testing has decided about the direction of conversion, the implementation is simple: I opted for a simple recursive concatenation in list_atom/3, that could be easily optimized, for instance adding an accumulator and thus making it tail recursion optimized, while atom_list/3 scan left to right looking for separator, and when it find it, store in list head and get the right part for recursion.
关于一个头脑简单的 DCG 实现，我用这段代码来测试一个很好的抽象列表//3 由 dcg_util，导致这个紧凑的代码:
About a simple minded DCG implementation, I used this code to test a nice abstraction list//3 implemented by dcg_util, leading to this compact code:
list_atom(L, Sep, Atom) :-
phrase(list(atom_codes, atom_codes(Sep), L), AtomCs),
atom_codes(Atom, AtomCs).
atom_codes(A) --> {atom_codes(A, Cs)}, Cs.
atom_list(Atom, Sep, L) :-
atom_codes(Atom, AtomCs),
phrase(list(any, atom_codes(Sep), LCs), AtomCs),
!, maplist(atom_codes, L, LCs).
any([]) --> [].
any([C|Cs]) --> [C], any(Cs).
很简单，无需列表即可直接实现//3...
Would be simple enough to directly implement without list//3...
这篇关于使用 SICStus 拆分原子，如 SWI 中的 atomic_list_concat/3的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！