type EvalState … type evalState … // NewEvalState returns an EvalState instanced used to observe the intermediate // evaluations of an expression. func NewEvalState() EvalState { … } // IDs implements the EvalState interface method. func (s *evalState) IDs() []int64 { … } // Value is an implementation of the EvalState interface method. func (s *evalState) Value(exprID int64) (ref.Val, bool) { … } // SetValue is an implementation of the EvalState interface method. func (s *evalState) SetValue(exprID int64, val ref.Val) { … } // Reset implements the EvalState interface method. func (s *evalState) Reset() { … }