Refactor state machine to XState-inspired declarative architecture

[Copilot]

Refactored the lexer state machine from imperative nested functions to a declarative configuration pattern inspired by XState.

Changes

• Declarative state configuration: Replaced 18 nested function definitions with a centralized configuration object using on (transitions) and def (default handlers)
• Type safety: Added explicit TypeScript interfaces for Context, Transition, Action, and StateHandler
• Pattern-based matching: Centralized character classification logic with reusable pattern matchers
• Code reduction: 453 → 243 lines (46% reduction)

Example

Before:

function K1(c: string) {
  if (isProperty(c)) {
    tokenString += c;
    return K1;
  }
  if (c === ".") {
    emit();
    tokenString = c;
    emit();
    return O2;
  }
  // ... 6 more if statements
  throw new Exception(index, `must be '.' or '(' or '[', not '${c}'`);
}

After:

K1: {
  on: {
    isProperty: { to: "K1", do: (c, ch) => { c.str += ch; } },
    ".": { to: "O2", do: (c, ch) => { c.emit(); c.str = ch; c.emit(); } },
    "(": { to: "O5", do: (c, ch) => { c.emit(TokenType.ID_FN); c.str = ch; c.emit(); } },
    // ... compact transition definitions
  },
  def: (c, ch) => { throw new Exception(c.idx, `must be '.' or '(' or '[', not '${ch}'`); }
}

All 33 existing tests pass without modification.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>refactor stater</issue_title> <issue_description>## Description 使用类似于xstate库去重构状态机。

Target

• [ ] 增加代码可读性
• [ ] 减少代码量</issue_description>

Comments on the Issue (you are @copilot in this section)

Custom agent used: Refactor Agent You are a js code refactoring master.

• Fixes Lydanne/ctxexp-parser#1

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