Improve types pkg (#668)

checker/checker_test.go

@@ -1074,7 +1074,7 @@ func TestCheck_types(t *testing.T) {
 	env := types.Map{
 		"foo": types.StrictMap{
 			"bar": types.Map{
-				"baz": "",
+				"baz": types.String,
 			},
 		},
 	}

checker/nature/of.go

@@ -1,47 +0,0 @@
-package nature
-
-import (
-	"fmt"
-	"reflect"
-
-	"github.com/expr-lang/expr/types"
-)
-
-func Of(value any) Nature {
-	if value == nil {
-		return Nature{Nil: true}
-	}
-
-	v := reflect.ValueOf(value)
-
-	switch v.Kind() {
-	case reflect.Map:
-		_, strict := value.(types.StrictMap)
-		fields := make(map[string]Nature, v.Len())
-		for _, key := range v.MapKeys() {
-			elem := v.MapIndex(key)
-			if !elem.IsValid() || !elem.CanInterface() {
-				panic(fmt.Sprintf("invalid map value: %s", key))
-			}
-			face := elem.Interface()
-			switch face.(type) {
-			case types.Map, types.StrictMap:
-				fields[key.String()] = Of(face)
-			default:
-				if face == nil {
-					fields[key.String()] = Nature{Nil: true}
-					continue
-				}
-				fields[key.String()] = Nature{Type: reflect.TypeOf(face)}
-
-			}
-		}
-		return Nature{
-			Type:   v.Type(),
-			Fields: fields,
-			Strict: strict,
-		}
-	}
-
-	return Nature{Type: v.Type()}
-}