The typed flow core

The decorator layer validates the graph at boot. The functional core, flow, validates it in the type checker — before the program ever runs.

import { flow } from '@green-tea/core';

const pipeline = flow()
  .step('db', () => ({ find: (id: string) => id }))
  .step('user', (ctx) => ctx.db.find('u1')); // referencing a missing 'db' would not compile

Each .step(name, fn) adds its output to the accumulated context type (Acc & Out). The next step’s ctx is typed with everything produced so far — so reading ctx.db compiles only because a previous step provided db. Reference a key nothing produced and it is a compile error, not a runtime undefined.

This is the strongest guarantee green-tea offers: the type is the dependency contract, checked statically. The decorator layer gives you the same graph with boot-time validation and the ergonomics of classes and decorators; flow gives you compile-time proof.

Note

npm run typecheck in the repo includes a type-level test that asserts this accumulation behaves — a step that reads a missing key is expected to fail compilation.

See The dependency graph for how both layers describe the same model.