如何递归地更改序言列表中的元组？

Question

I have a list in the following format:

[(index, count, color),(index+1,newcount,othercolor),...]

And I want, having an ordered list with an index given, change the count value of the tuple with that index.

What I've done so far is:

play(Index,[(Index,Count,Color)|T], [(Index,NewCount,Color)|T]):-

    NewCount is Count + 1.


play(Index,[Tuple|T],[Tuple|T]):-

    play(Index,T,T).

It just gives me no...

Any suggestions?

Thanx for any answer!

Answer 1

since you want to create a different list, you cannot say at the second clause of the predicate will be the same. Instead, you should use a new variable for the new tail. Something like:

play(Index,[(Index,Count,Color)|T], [(Index,NewCount,Color)|T]):-
    NewCount is Count + 1.


play(Index,[Tuple|T1],[Tuple|T2]):-    
    play(Index,T1,T2).                

Answer 2

Because you know it's sorted, you can fail early in case Index is not in the list.

play(Index,[(Index,Count,Color)|T], [(Index,NewCount,Color)|T]) :-
  NewCount is Count + 1.
play(Index,[(IndexT,_,_)|_], _) :-
  Index < IndexT, !, fail.
play(Index,[Tuple|T1],[Tuple|T2]) :-
  play(Index,T1,T2).

Allowing the inefficiency above, you could be interested in a possible solution that uses standard builtins for list manipulation.

play_bt(Index, Old, New) :-
  append(Left, [(Index, Count, Color)|Rest], Old),
  NewCount is Count + 1,
  append(Left, [(Index, NewCount, Color)|Rest], New).