better-context: Skill for Codex

better-result Adoption

Migrate existing error handling (try/catch, Promise rejections, thrown exceptions) to typed Result-based error handling with better-result.

When to Use

• Adopting better-result in existing codebase
• Converting try/catch blocks to Result types
• Replacing thrown exceptions with typed errors
• Migrating Promise-based code to Result.tryPromise
• Introducing railway-oriented programming patterns

Migration Strategy

1. Start at Boundaries

Begin migration at I/O boundaries (API calls, DB queries, file ops) and work inward. Don't attempt full-codebase migration at once.

2. Identify Error Categories

Before migrating, categorize errors in target code:

Category	Example	Migration Target
Domain errors	NotFound, Validation	TaggedError + Result.err
Infrastructure	Network, DB connection	Result.tryPromise + TaggedError
Bugs/defects	null deref, type error	Let throw (becomes Panic if in Result callback)

3. Migration Order

1. Define TaggedError classes for domain errors
2. Wrap throwing functions with Result.try/tryPromise
3. Convert imperative error checks to Result chains
4. Refactor callbacks to generator composition

Pattern Transformations

Try/Catch to Result.try

// BEFORE
function parseConfig(json: string): Config {
  try {
    return JSON.parse(json);
  } catch (e) {
    throw new ParseError(e);
  }
}

// AFTER
function parseConfig(json: string): Result<Config, ParseError> {
  return Result.try({
    try: () => JSON.parse(json) as Config,
    catch: (e) => new ParseError({ cause: e, message: `Parse failed: ${e}` }),
  });
}

Async/Await to Result.tryPromise

// BEFORE
async function fetchUser(id: string): Promise<User> {
  const res = await fetch(`/api/users/${id}`);
  if (!res.ok) throw new ApiError(res.status);
  return res.json();
}

// AFTER
async function fetchUser(id: string): Promise<Result<User, ApiError | UnhandledException>> {
  return Result.tryPromise({
    try: async () => {
      const res = await fetch(`/api/users/${id}`);
      if (!res.ok) throw new ApiError({ status: res.status, message: `API ${res.status}` });
      return res.json() as Promise<User>;
    },
    catch: (e) => (e instanceof ApiError ? e : new UnhandledException({ cause: e })),
  });
}