list - Prolog中列表的条件解析

Question

考虑这三个列表:

["cal"]          %Execute Condition 1 if list 1 is passed 
["cal",2,1947]   %Execute Condition 2 if List 2 is passed
["Hello","World","Random","List"] %Do not execute anything

如果列表 1 通过，则预期的输出

calendar(1, 2016)

如果列表 2 通过，则预期输出

calendar(2, 1947)

到目前为止我的代码

% Execute this predicate for condition 2
cal(X,Y,Z1,Z2) :-
   Z1 is X,
   Z2 is Y.

% Executed this predicate for condition 1
cal(Z1,Z2) :-
   monthyear(Z1,Z2).

monthyear(M,Y) :-
   get_time(Stamp),
   stamp_date_time(Stamp, DateTime, local),
   date_time_value(month, DateTime, M),
   date_time_value(year, DateTime, Y).

如何完成我的代码以支持所需的功能？我尝试过的:

parentcal(X,Y) :-
   X = [H1|T1],
   H1 is "cal",
   T1 = [H2|T2],
   T3 = [H3|T3],
   cal(H2, H3, M, Y),
   write("calendar("),
   write(M),
   write(" "),
   write(Y),
   write(")").

parentcal(X,Y) :-
   X = [H1|T1],
   H1 is "cal",
   T1 = [H2|T2],
   H2 is null,
   T3 = [H3|T3],
   H3 is null,
   cal(M, Y),
   write("calendar("),
   write(M),
   write(" "),
   write(Y),
   write(")").

Answer 1

也许我遗漏了什么，但它似乎不应该比这样的东西复杂得多:

do_something( [cal] , R ) :-
  get_time(TS) ,
  stamp_date_time(TS,DT,local) ,
  date_time_value(month,M) ,
  date_time_value(year,Y) ,
  do_something( [cal,M,Y] , R )
  .
do_something( [cal,M,Y] , calendar( M , Y ) ) :-
  int(M) ,
  between(1,12,M) ,
  int(Y) ,
  Y > 0
  .