operator-context.go: now supports contextes that implement the Formatter interface

operator-context.go

@@ -31,6 +31,9 @@ func evalContextValue(ctx ExprContext, self *term) (v any, err error) {
 	}
 
 	if sourceCtx != nil {
+		if formatter, ok := ctx.(Formatter); ok {
+			v = formatter.ToString(0)
+		} else {
 			keys := sourceCtx.EnumVars(func(name string) bool { return name[0] != '_' })
 			d := make(map[string]any)
 			for _, key := range keys {
@@ -41,6 +44,7 @@ func evalContextValue(ctx ExprContext, self *term) (v any, err error) {
 				d[key], _ = sourceCtx.GetFuncInfo(key)
 			}
 			v = d
+		}
 	} else {
 		err = self.errIncompatibleType(childValue)
 	}