pattern-schema

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Schema Design Phase

Goal

Create schemas.tsx with all data types and Input/Output types BEFORE any pattern code.

Read First

• docs/common/concepts/types-and-schemas/default.md
• docs/common/concepts/types-and-schemas/writable.md
• docs/common/concepts/pattern.md (Input/Output section)

Rules

1. ALWAYS use pattern<Input, Output>() - Never use single-type pattern<State>(). Single-type patterns cannot be tested via .send().
2. Every editable field needs Writable<> in Input type (for write access)
3. Output types never use Writable<> - they reflect returned data shape
4. Fields that could be undefined initially: use Default<T, value>
5. Actions in Output type: Stream<T> (enables testing and linking)
6. Sub-patterns need [NAME]: string and [UI]: VNode in Output type

Template

import { Default, NAME, Stream, UI, VNode, Writable } from "commontools";

// ============ DATA TYPES ============
export interface Item {
  name: Default<string, "">;
  done: Default<boolean, false>;
}

// ============ PATTERN INPUT/OUTPUT ============
export interface ItemInput {
  item: Writable<Item>;  // Writable in Input = pattern will modify
}

export interface ItemOutput {
  [NAME]: string;        // Required for sub-patterns
  [UI]: VNode;           // Required for sub-patterns
  item: Item;            // No Writable in Output
  toggle: Stream<void>;  // Actions as Stream<T>
}

Done When

• All data types defined with correct Writable/Default wrapping
• All Input/Output types defined for each sub-pattern
• No TypeScript errors: deno task ct check schemas.tsx --no-run