Inferencing

the set of type variables of the current typer state that cannot be interpolated at the present time Eligible for interpolation are all type variables owned by the current typerstate that are not in locked and whose nestingLevel is >= ctx.nestingLevel. Type variables occurring co- (respectively, contra-) variantly in the tree type or expected type are minimized (respectvely, maximized). Non occurring type variables are minimized if they have a lower bound different from Nothing, maximized otherwise. Type variables appearing non-variantly in the type are left untouched. Note that even type variables that do not appear directly in a type, can occur with some variance in the type, because of the constraints. E.g if X occurs co-variantly in T and we have a constraint Y <: X Then Y also occurs co-variantly in T because it needs to be minimized in order to constrain T the least. See variances for more detail.

the expected result type

the tree whose type is interpolated