@onrails/maybe

Tagged Maybe for expected absence — cache miss, optional field, not-ready-yet. Not for failures (use @onrails/result).

Install

bun add @onrails/maybe

Usage

import { compactMap, fromNullable, isSome, match, some } from "@onrails/maybe";

const row = fromNullable(db.get(id));

const name = match(
  row,
  (r) => r.name,
  () => "guest",
);

Side effects

tap runs an effect on the Some value, tapNone on absence — both pass the Maybe through unchanged. Mirrors tap/tapErr from @onrails/result. Dual-form.

import { fromNullable, tap, tapNone } from "@onrails/maybe";

const row = fromNullable(db.get(id));

tap(row, (r) => log.debug("hit", r.id)); // runs on Some, returns row
tapNone(row, () => metrics.miss());       // runs on None, returns row

Result boundary

import { toResult } from "@onrails/maybe/interop";

const user = toResult(fromNullable(row), () => ({ kind: "not_found" as const }));

Subpaths

| Path | Contents | |------|----------| | @onrails/maybe | Core | | @onrails/maybe/fluent | fluent(maybe) chains | | @onrails/maybe/interop | toResult, fromResult, NoneError |

See DESIGN.md.