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Why are compound terms preferable over lists in terms of performance? For example,
matrix(row(1,2,3),row(1,2,3),row(1,2,3))
is preferable over
[[1,2,3],[1,2,3],[1,2,3],[1,2,3]]
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In Prolog, a compound term of the form is usually pictured as a tree in which every node contains the name of the functor of the term and has exactly children each one of which is the root of the tree of terms .
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.
You just want the last element of the list. Try this: lastElement([Head]) :- write(Head). lastElement([_|Tail]):- lastElement(Tail).
First, just to be clear: Lists are a kind of compound term.
To see what lists are, use write_canonical/1. For example, using GNU Prolog:
| ?- write_canonical([1,2,3]).
'.'(1,'.'(2,'.'(3,[])))
Regarding representation in memory, I recommend Richard O'Keefe's book. The details differ between systems, but you can be pretty sure that to represent the term row(1,2,3) in memory, you need:
For the term .(1, .(2, .(3, []) in a straight-forward memory representation, you need:
'.'/2 functors[]).From this, you already see that using lists takes at least roughly twice as much memory in this representation.
A few simple tests that you can carry out yourself will help you to see the difference in memory consumption of these representations for your system.
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