moved a subset of source file to the kern package

operator-unset.go

@@ -4,7 +4,11 @@
 // operator-unset.go
 package expr
 
-import "strings"
+import (
+	"strings"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
 
 //-------- unset term
 
@@ -18,7 +22,7 @@ func newUnsetTerm(tk *Token) (inst *term) {
 	}
 }
 
-func deleteContextItem(ctx ExprContext, opTerm *term, item any) (deleted bool, err error) {
+func deleteContextItem(ctx kern.ExprContext, opTerm *term, item any) (deleted bool, err error) {
 	if name, ok := item.(string); ok {
 		var size int
 		if strings.HasSuffix(name, "()") {
@@ -31,12 +35,12 @@ func deleteContextItem(ctx ExprContext, opTerm *term, item any) (deleted bool, e
 			deleted = ctx.VarCount() < size
 		}
 	} else {
-		err = opTerm.errIncompatibleType(item)
+		err = opTerm.errIncompatiblePrefixPostfixType(item)
 	}
 	return
 }
 
-func evalUnset(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalUnset(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 	var childValue any
 	var deleted bool
 
@@ -45,8 +49,8 @@ func evalUnset(ctx ExprContext, opTerm *term) (v any, err error) {
 	}
 
 	count := 0
-	if IsList(childValue) {
-		list, _ := childValue.(*ListType)
+	if kern.IsList(childValue) {
+		list, _ := childValue.(*kern.ListType)
 		for _, item := range *list {
 			if deleted, err = deleteContextItem(ctx, opTerm, item); err != nil {
 				break