type mismatch in prolog code

Question

I have written a rule like below:

rule_1561_cctype([],_,_,_).
rule_1561_cctype([X1|Y1],[Ru1|Ru1T],[Ru2|Ru2T],[Ru3|Ru3T]):-
    X1 is 0 -> Ru1 in {2,3,4}, Ru2 in {-1}, Ru3 in {-1}
    ;X1 is 1 -> Ru1 in {2,3,4}, Ru2 in {2,3,4}, Ru3 in {-1}
  ;X1 is 2 -> Ru1 in {2}, Ru2 in {2}, Ru3 in {2}
  ;rule_1561_cctype(Y1,Ru1,Ru2,Ru3),!.

i am calling this rule like below:

rule_1561_cctype(CctypeInt, Ru1, Ru2,Ru3),

where CctypeInt is integer list.

but i am getting an error below:

      935      9 Call: rule_1561_cctype(dom(0..2),dom({-1}\/(2..4)),dom({-1}\/(2..4)),dom({-1}\/(2..4))) ? 
! Type error in argument 2 of = /2
! integer expected, but [] found
! goal:  _310957=[]
      935      9 Exception: rule_1561_cctype(dom(0..2),dom({-1}\/(2..4)),dom({-1}\/(2..4)),dom({-1}\/(2..4))) ? 

am i wrong somewhere?

Answer 1

You are doing constraint logic programming, right? The problem is that Prolog tries to unify a constrained variable ranging over a numeric with an empty list and reports an error.

Looking at your code I presume that the call to rule_1561_cctype(Y1,Ru1,Ru2,Ru3) should be rule_1561_cctype(Y1,Ru1T,Ru2T,Ru3T).