How to find the positive numbers in a list in Prolog? -


i want write code in prolog gets list , find positive numbers , adds them new list below : 

?- findpositives([-1,2,3,-5,-7,9],result) result : [2,3,9]

how can write code?

using tfilter/3:

positive_truth(n, true) :-    n >= 0. positive_truth(n, false) :-    n < 0.  ?- tfilter(positive_truth, [-1,2,3,-5,-7,9],result). result = [2,3,9]

alternatively, using library(clpfd):

pos_truth(expr, truth) :-    expr #>= 0 #<==> bool,    bool01_truth(bool, truth).  bool01_truth(0,false). bool01_truth(1,true).  ?- tfilter(pos_truth, [-1,2,3,-5,-7,9],result). result = [2,3,9].  ?- tfilter(pos_truth, [x,y],result).    result = [],     x in inf.. -1, y in inf.. -1 ;  result = [y],    x in inf.. -1, y in 0..sup ;  result = [x],    x in 0..sup,   y in inf.. -1 ;  result = [x, y], x in 0..sup,   y in 0..sup.

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