moved a subset of source file to the kern package

t_builtin-fmt_test.go

@@ -9,6 +9,8 @@ import (
 	"bytes"
 	"fmt"
 	"testing"
+
+	"git.portale-stac.it/go-pkg/expr/kern"
 )
 
 func TestFuncFmt(t *testing.T) {
@@ -37,11 +39,11 @@ func TestFmt(t *testing.T) {
 
 	var b bytes.Buffer
 	ctx := NewSimpleStore()
-	currentStdout := SetCtrl(ctx, ControlStdout, &b)
+	currentStdout := kern.SetCtrl(ctx, kern.ControlStdout, &b)
 
 	runCtxTestSuite(t, ctx, section, inputs)
 
-	SetCtrl(ctx, ControlStdout, currentStdout)
+	kern.SetCtrl(ctx, kern.ControlStdout, currentStdout)
 	if b.String() != text+"\n" {
 		t.Errorf("println(): Got: %q, Want: %q", b.String(), text+"\n")
 	}