Introduction to Prolog and Computational Linguistics -- Indentation

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Indentation

To make programs easier to read, you should always indent the goals of rules. If you typed in your procedure for intersection as follows, it would look like a series of facts:

% intersection/3
 
intersection([],_,[]):- !.
 
intersection([H|T],L,[H|T2]):-
member(H,L),!,
intersection(T,L,T2).
 
intersection([_H|T],L,T2):-
intersection(T,L,T2).

If you indent the goals, it is much clearer what is a fact and what is a rule:

% intersection/3
 
intersection([],_,[]):- !.
 
intersection([H|T],L,[H|T2]):-
        member(H,L),!,
        intersection(T,L,T2).
 
intersection([_H|T],L,T2):-
        intersection(T,L,T2).

You can indent goals by using the tab key. Emacs recognises files that end in .pl and will automatically move the cursor to a suitable place for the goal.

<a.von.klopp@bangor.ac.uk>