Passing functions when creating constraints on top of classifiers

[danyaljj]

How can we pass functions on top of classifier constraints? For example we can do sth like:

(C1 on i1).is("blah")

Can we pass a function f: String => String (e.g. substring):

(f(C1 on i1)).is("blah")

Similarly, currently we can add equality for two classifiers:

(C1 on i1).is(C2 on i2)

How can we pass functions f: String => String for this equality constraints?

(f1(C1 on i1)).is(f2(C2 on i2))

[kordjamshidi]

isn't this issue related to #167 which is assigned to @danyaljj ?

[kordjamshidi]

related to #167