distance((X,Y), D) :- D is X * X + Y * Y.

distance_sort(L, S) :-
    map_list_to_pairs(distance, L, P),
    keysort(P, SP), pairs_values(SP, S).
	
:-  L = [(1,2), (3,4), (1,3), (2,4), (1,8)],
    msort(L, S1), writeln(S1),
    distance_sort(L, S2), writeln(S2).