Enumerating domains in Prolog's clpfd -

i'm exploring dependent structures of constraints one:

assign(x,y) :-      x in 1..5,      ((x mod 2 #= 1) #=> y in 2..3),      ((x mod 2 #= 0) #=> y #= 5). 

what i'm looking representation of x's , y's domains sparse possible - in case along lines of x in {1,3,5} , y in {2,3} or x in {2,4} , y = 5.

one way of doing detect variables on left side of #=>, enumerate values , collect , merge them together, ?- assign(x, y), findall(x-d, (indomain(x),fd_dom(y,d)), c), stuff c, maybe there more efficient way?

i've encountered error trying label([x,y]): arguments not sufficiently instantiated goes away when add constraint on y's domain.

when should expect error occur? feel have poor understanding of clpfd's mechanisms , limitations, there resources learn from? know basics of constraint programming, arc consistency etc.

to keep clpfd enumeration predicates (like indomain/1, label/1, labeling/2, etc.) ever throwing instantiation errors, ensure all variables have been assigned finite domain before enumeration predicates executed.

so how directly translating wrote code?

assign(x,y) :- x in 1\/3\/5, y in 2..3.     %    x in {1,3,5} , y in {2,3}  assign(x,y) :- x in 2..4,    y in 5.        % or x in {2,4}   , y = 5 

a simple query (with swi-prolog):

?- assign(x,y), labeling([],[x,y]).   x = 1, y = 2 ; x = 1, y = 3 ; x = 3, y = 2 ; x = 3, y = 3 ; x = 5, y = 2 ; x = 5, y = 3 ; x = 2, y = 5 ; x = 3, y = 5 ; x = 4, y = 5.