Is it possible to delay an assignment operation

Question

I have a small script/code and i want to impose some active constraints. In the code shown below, i have P[I,J] #= E and in the next line Result[I,E] #= J but this is throwing an instantiation error because E is not instantiated.

For these constraints i need to know what value is at P[I,J], so if i write it as E is P[I,J] then offcourse i will not get an instantiation error(incase i suspend next two constraints with suspend, e.g suspend:(P[I,J] #= E) but will it effect the activeness of a constraint because the assignment will not be delayed but only constraint will be delayed. Is there any alternative way to impose this constraint?

multifor([I,J] ,[1,1],[N,N]),param(P,ResultFirst),foreach(E,_) do
            E #:: 1..9,
            P[I,J] #= E,
           (ResultFirst[I,E] #= J),

Answer 1

It would be nice if one could just write it the way you have done, but unfortunately this is currently not supported (assuming you are using ECLiPSe). If the array index E is uninstantiated at constraint setup time, you have to use an element/3 constraint. So, instead of

ResultFirst[I,E] #= J

write

element(E, ResultFirst[I], J)