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You can express the above in Prolog like so: update([],[],[]). update([[X,_]|Xs],[Y|Ys],[[X,Y]|XYs]) :- update(Xs,Ys,XYs).
maplist/2 and maplist/3 are higher-order predicates, which allow the definition of a predicate to be lifted about a single element to lists of such elements. These predicates can be defined using call/2 and call/3 as building blocks and ship with many Prolog systems.
You can move unification into the head of the clause and simply write: second([_, Second| _], Second). The notation for lists is to write the initial elements separated by commas and then a vertical bar to separate the list tail, i.e. the list containing the rest of the elements.
In Prolog list elements are enclosed by brackets and separated by commas. Another way to represent a list is to use the head/tail notation [H|T]. Here the head of the list, H, is separated from the tail of the list, T, by a vertical bar. The tail of a list is the original list with its first element removed.
I'd like to have a Prolog predicate that can replace an element in a list at a specified index.
Example:
% replace(+List,+Index,+Value,-NewList).
?- L=[a,b,c,d], replace(L,1,z,L2).
L2 = [a,z,c,d]
I don't know how to do this. Thanks for your help! Loïc.
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