CODEWITHSUNDEEP
prologrepeat
user2880113
user2880113

Reputation: 355

Prolog- repeat input until

I want to create a predicate that only accepts a specific input from the user and it will keep asking for the right input if the user gives the wrong input. I've created this, but its not completed because it does not ask for the new input if its wrong:

askchar(X):- write('give char'),nl, get_char(X), test(X).

test(X):- X=a, write('ok'). %accepts a
test(X):- X='1', write('ok'). %accepts 1
test(X):- write('wrong input. try again'),nl.

Upvotes: 1

Views: 2998

Answers (2)

User
User

Reputation: 14873

Here is what I got:

askChar(Char) :- get_char(Char), test(Char), write('This is the right char, thank you.'), !.
askChar(Char) :- write('That is wrong char!'), askChar(Char).    

test(s).

It asks again and again until the char s is typed in.

Upvotes: 1

CapelliC
CapelliC

Reputation: 60014

in systems lacking a decent tail recursive optimization, processing side effects can be conveniently done with a failure driven loop

1 ?- [user].
|: askchar(C) :- repeat, get(C), (C = 0'a ; C = 0'1, ! ; fail).
% user://1 compiled 0.07 sec, 2 clauses
true.

2 ?- askchar(X).
|: 5
|: a

X = 97 .

Upvotes: 2

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