moved a subset of source file to the kern package

operator-range.go

@@ -4,7 +4,11 @@
 // operator-range.go
 package expr
 
-import "fmt"
+import (
+	"fmt"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
+)
 
 // -------- range term
 type intPair struct {
@@ -12,10 +16,10 @@ type intPair struct {
 }
 
 func (p *intPair) TypeName() string {
-	return TypePair
+	return kern.TypePair
 }
 
-func (p *intPair) ToString(opt FmtOpt) string {
+func (p *intPair) ToString(opt kern.FmtOpt) string {
 	return fmt.Sprintf("(%d, %d)", p.a, p.b)
 }
 
@@ -41,21 +45,21 @@ func changeColonToRange(t *term) {
 	}
 }
 
-func evalRange(ctx ExprContext, opTerm *term) (v any, err error) {
+func evalRange(ctx kern.ExprContext, opTerm *term) (v any, err error) {
 	var leftValue, rightValue any
 
 	if len(opTerm.children) == 0 {
 		leftValue = int64(0)
 		rightValue = int64(-1)
 	} else if len(opTerm.children) == 1 {
-		if leftValue, err = opTerm.children[0].compute(ctx); err != nil {
+		if leftValue, err = opTerm.children[0].Compute(ctx); err != nil {
 			return
 		}
-		rightValue = int64(ConstLastIndex)
+		rightValue = int64(kern.ConstLastIndex)
 	} else if leftValue, rightValue, err = opTerm.evalInfix(ctx); err != nil {
 		return
 	}
-	if !(IsInteger(leftValue) && IsInteger(rightValue)) {
+	if !(kern.IsInteger(leftValue) && kern.IsInteger(rightValue)) {
 		// err = opTerm.errIncompatibleTypes(leftValue, rightValue)
 		err = errRangeInvalidSpecification(opTerm)
 		return