为什么在使用带有lambda和tilde项的maplist时会出现无限循环?

我有几个谓词使用
lambda,波段术语从
func,lambda和func,以及最后“纯Prolog”同时没有lambda和func做同样的事情:

:- use_module(library(lambda)).
:- use_module(library(func)).

both_lambda_and_func :-
    maplist(\X^(print(length(X,~))), [`one`,`two`,`three`]).

lambda_only :-
    maplist(\X^(length(X,Len),print(Len)), [`one`,`two`,`three`]).

func_only :-
    maplist(func_only_helper, [`one`,`two`,`three`]).
func_only_helper(X) :-
    print(length(X,~)).

normal_prolog :-
    maplist(normal_prolog_helper, [`one`,`two`,`three`]).
normal_prolog_helper(X) :-
    length(X,Len),
    print(Len).

所有谓词都应打印335(列表中的字符串长度),其中三个正确执行.问题是both_lambda_and_func / 0没有打印任何东西,似乎进入无限循环.我试图追踪/ 0问题,但对我来说似乎太复杂了.你能告诉我,如果我做错了,或者这可能是一个奇怪的错误吗?我正在使用SWI-Prolog 7.1.14,func 0.0.4,lambda 1.0.0.

最佳答案

?- listing(both_lambda_and_func).
both_lambda_and_func :-
    length(A, B),
    maplist(\A^print(B),
        [[111, 110, 101], [116, 119, 111], [116, 104, 114, 101, 101]]).

在错误的背景下,无法表达盲目重写的术语范围.程序不会终止,因为length / 2有两个参数都是空闲的,然后生成更长的列表.

[trace] 4 ?- both_lambda_and_func.
   Call: (6) both_lambda_and_func
   Call: (7) length(_G1485, _G1486)
   Exit: (7) length([], 0)
^  Call: (7) apply:maplist(\[]^print(0), [[111, 110, 101], [116, 119, 111], [116, 104, 114, 101|...]])
   Call: (8) apply:maplist_([[111, 110, 101], [116, 119, 111], [116, 104, 114, 101|...]], user: \[]^print(0))
^  Call: (9) lambda: \([]^print(0), [111, 110, 101])
   Call: (10) copy_term_nat(user:[]^print(0), _G1541)
   Exit: (10) copy_term_nat(user:[]^print(0), user:[]^print(0))
^  Call: (10) lambda: ^([], print(0), [111, 110, 101])
^  Fail: (10) lambda: ^([], user:print(0), [111, 110, 101])
^  Fail: (9) lambda: \(user:[]^print(0), [111, 110, 101])
   Fail: (8) apply:maplist_([[111, 110, 101], [116, 119, 111], [116, 104, 114, 101|...]], user: \[]^print(0))
^  Fail: (7) apply:maplist(user: \[]^print(0), [[111, 110, 101], [116, 119, 111], [116, 104, 114, 101|...]])
   Redo: (7) length(_G1485, _G1486)
   Exit: (7) length([_G1478], 1)
^  Call: (7) apply:maplist(\[_G1478]^print(1), [[111, 110, 101], [116, 119, 111], [116, 104, 114, 101|...]])
   Call: (8) apply:maplist_([[111, 110, 101], [116, 119, 111], [116, 104, 114, 101|...]], user: \[_G1478]^print(1))
^  Call: (9) lambda: \([_G1478]^print(1), [111, 110, 101])
   Call: (10) copy_term_nat(user:[_G1478]^print(1), _G1547)
   Exit: (10) copy_term_nat(user:[_G1478]^print(1), user:[_G1546]^print(1))
^  Call: (10) lambda: ^([_G1546], print(1), [111, 110, 101])
^  Fail: (10) lambda: ^([_G1546], user:print(1), [111, 110, 101])
...

对^的调用出错了

^  Fail: (10) lambda: ^([], user:print(0), [111, 110, 101])

因为X已经实例化为[],而应该是免费的……

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