CODEWITHSUNDEEP
listprolog
Gilgamesz
Gilgamesz

Reputation: 5073

Lists of N length

Is it to possible to create N elements of 0 array in another way than the following one:

makeInitialArray(N, A) :-
   N > 0,
   Nn is N-1,
   makeInitialArray(Nn, B),
   append([0], B, A).
makeInitialArray(0, []).

It is a poor way on my eye because of the fact of recurrence. I suppose that will be made to call very often operation like that.

Upvotes: 1

Views: 44

Answers (1)

repeat
repeat

Reputation: 18726

Keep it simple! How? Delegate the "recursive part" to built-in / library predicates!

Based on length/2, maplist/2, and (=)/2 define n_zeroes/2:

:- use_module(library(lists), [maplist/2]).

n_zeroes(N, Zs) :-
   length(Zs, N),
   maplist(=(0), Zs).

Sample queries using SICStus Prolog 4.3.2:

| ?- n_zeroes(10, Zs).
Zs = [0,0,0,0,0,0,0,0,0,0] ? ;
no
| ?- n_zeroes(N, Zs).
N = 0, Zs = [] ? ;
N = 1, Zs = [0] ? ;
N = 2, Zs = [0,0] ? ;
N = 3, Zs = [0,0,0] ? ;
N = 4, Zs = [0,0,0,0] ? ;
N = 5, Zs = [0,0,0,0,0] ? 
...                             % ...goes on forever and ever...

Upvotes: 3

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