moved a subset of source file to the kern package

operator-iter-value.go

@@ -4,6 +4,10 @@
 // operator-iter-value.go
 package expr
 
+import (
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
+
 //-------- iter value term
 
 func newIterValueTerm(tk *Token) (inst *term) {
@@ -16,17 +20,17 @@ func newIterValueTerm(tk *Token) (inst *term) {
 	}
 }
 
-func evalIterValue(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalIterValue(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 	var childValue any
 
 	if childValue, err = opTerm.evalPrefix(ctx); err != nil {
 		return
 	}
 
-	if it, ok := childValue.(Iterator); ok {
+	if it, ok := childValue.(kern.Iterator); ok {
 		v, err = it.Current()
 	} else {
-		err = opTerm.errIncompatibleType(childValue)
+		err = opTerm.errIncompatiblePrefixPostfixType(childValue)
 	}
 	return
 }