DCG problem

[confusedstudent1]

I have to write a DCG that generates strings from the alphabet a E {0,1,2} the strings have to have the form nn. This means queries like ?- s([0,2,1,0,2,1],[]). and s([1,1,2,0,1,1,2,0],[]). would return true.

This is the code I have so far. I'm so close. Can someone help me further?


s --> s(X), s(X).
s --> [].

s(0) --> zero, s(X).
s(1) --> one, s(X).
s(2) --> two, s(X).
s(3) --> [].

zero --> [0].
one --> [1].
two --> [2].


Many thanks

 

[kahleen]

s --> [].
s --> sx, s.

sx --> [0].
sx --> [1].
sx --> [2].

 

[joel76]

You are very close to the solution !

Just look at these rules
s --> s(X), s(X).
and
s(0) --> zero, s(X).

In the first rule, what is the type of X, an atom or a list ?
In the second rule you use an atom 0, and you introduce X in the body of the rule. You don't have a lot of things to change/add.

 

[joel76]

No kahleen the production must have the form nn, you accept [0,1,2] for example.

 

[confusedstudent1]

Great! Thanks joel! I got it!