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

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).
``````

``````?- 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]]).
``````

``````[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])
...
``````

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