New interface to Typer: the function TypeName() returns a more readable type name

formatter.go

@@ -4,6 +4,8 @@
 // formatter.go
 package expr
 
+import "fmt"
+
 type FmtOpt uint16
 
 const (
@@ -18,3 +20,16 @@ const (
 type Formatter interface {
 	ToString(options FmtOpt) string
 }
+
+type Typer interface {
+	TypeName() string
+}
+
+func getTypeName(v any) (name string) {
+	if typer, ok := v.(Typer); ok {
+		name = typer.TypeName()
+	} else {
+		name = fmt.Sprintf("%T", v)
+	}
+	return
+}