Question

仅运行单个谓词时，程序将正确处理用户输入。

【代码】

main:-
    chooseusertype.

chooseusertype:-
    write('Log in as a merchant or customer?: '),
    read(X),
    format('Your log in type: ~w', [X]).

【执行结果】

Log in as a merchant or customer?: customer.
Your log in type: customer

但是，当我尝试将selectusertype谓词中给出的输入传递给startas谓词

【代码】

main(-Usertype):-
    chooseusertype,
    startas(Usertype).

chooseusertype:-
    write('Log in as a merchant or customer?: '),
    read(X),
    format('Your log in type: ~w', [X]).

startas('merchant'):-
    write('Logged in as merchant'), nl,
    write('Any update on the shelves?').

startas('customer'):-
    write('Logged in as customer'), nl,
    write('Let us help you find the ingredients you want!').

【执行结果】

false

失败。我知道语法不正确，但是我找不到任何Prolog文档写得很好，因此我陷入了困境。我该如何解决？

Answer 1

您可以像这样修改main和chooseusertype，这样的read/1返回选择的选项：

main:-
    chooseusertype(Usertype),
    startas(Usertype).

chooseusertype(X):-
    write('Log in as a merchant or customer?: '),
    read(X),
    format('Your log in type: ~w', [X]).

来自SWI documentation：

read(-Term)从当前输入流中阅读下一个Prolog术语并与Term
统一

此外，如果要打印错误消息，可以执行以下操作：

main:-
    chooseusertype(Usertype),
    ( startas(Usertype) -> 
        true; 
        format('~nUser type not recognised: ~w', [Usertype]),
        fail
    ).

?- main.
Log in as a merchant or customer?: asd.
Your log in type: asd
User type not recognised: asd
false.

将返回值从谓词传递到Prolog中的另一个谓词

1 个答案: