error callback

lib/Option.ts

@@ -19,6 +19,11 @@ interface Option {
   message?: string;
   preset?: unknown[];
   error?: string;
+  error_callback?: (
+    option: string,
+    value: unknown,
+    e: Error
+  ) => unknown;
 }
 
 interface OptionProcess extends Option {

lib/Sources/OptionSource.ts

@@ -19,7 +19,8 @@ export abstract class OptionSource {
       opt.filled = true;
     }
     catch (e) {
-      // could not assign
+      if (typeof opt.error_callback !== 'undefined')
+        opt.error_callback (opt.name, value, e);
     }
   }
 }