import type { Mod } from "../mod/index.js";
import type { Span } from "../span/index.js";
/**

   # Stmt and Command Pattern

   A `Stmt` is like a method of `Mod`,
   but implemented as an independent Command class.

   Unlike `Exp`, `Core`, `Value` and `Neutral`,
   which are closed ADT that will **not** be extended often.
   `Stmt` is an open abstract class that will be extended more often.

   Unlike functions about `Exp`, `Core`, `Value` and `Neutral`,
   which are pure, `stmt.execute` does side effects on `mod`.

**/
export declare abstract class Stmt {
    abstract span?: Span;
    abstract execute(mod: Mod): Promise<string | void>;
    undo(mod: Mod): void;
}
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