Sequences in Prolog

[jodders]

I need help with sequences where you can have a sequence of three letters eg. R,G,B in any order. The only two problems are letters are not allowed twice in sucession and G,B,R is not allowed in sucession.

Really need help

 

[slackerbrad]

Assuming you're representing the sequences as lists of r,g, and b (since prolog interprets capitals as variables), and you want to accept an empty sequence, you want something like:

gbr(g,b,r).
accept([]).
accept([X]).
accept([X,Y]):-X /== Y.
accept([X,Y,Z|Xs]):-
X /== Y,
not gbr(X,Y,Z),
accept([Y,Z|Xs]).