Module status

Pattern matching for values that can be in one of several exclusive states.

Use when working with data where exactly one variant is active at a time - like operation results that are either successful or failed, UI states that are loading, ready, or error, or any domain model where alternatives are mutually exclusive.

The Status function lets you handle each state with a dedicated handler, while TypeScript ensures all states are covered and values are accessed safely. Eliminates verbose conditional logic and prevents bugs from unhandled cases.

Usage

import { status, Condition } from '@metreeca/core/status';

// Define condition patterns for form field state

type FieldState = {
  unset: void;
  value: string;
  error: Error;
};

// Create status matcher (for example, for value condition)

const matcher = status<FieldState>({
  value: "user@example.com"
});

// Pattern match with function handlers

const message = matcher({
  unset: () => "Enter email",
  value: (email) => `Email: ${email}`,
  error: (err) => `Error: ${err.message}`
});

// Use constant handlers

const isValid = matcher({
  unset: false,
  value: true,
  error: false
});

// Use fallback for partial matching

const display = matcher({
  value: (email) => email
}, "‹blank›");
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