Fetch is a Scala library for simple and efficient data access, built on cats-effect. It provides a monadic abstraction (`Fetch[F, A]`) that automatically optimizes data fetching through batching, caching, deduplication, and parallel execution. Users define data sources by implementing the `DataSource` trait, specifying how to fetch individual identities or batches. The library then composes fetches using standard monadic and applicative combinators, transparently batching requests to the same source and running independent fetches concurrently. It supports custom caches, optional fetches, error handling, and debugging via a separate `fetch-debug` module. The architecture is a pure library with no runtime dependencies beyond cats-effect, making it suitable for both JVM and Scala.js. Key entry points include `Fetch.apply`, `Fetch.run`, `Fetch.runLog`, and `Fetch.runCache`. External dependencies are minimal: cats-effect, cats-core, and scalatest for testing.
Direct File is a full-stack, multi-service tax preparation and electronic filing system built by the IRS for federal and state tax returns. The architecture is a microservices monorepo with a Spring Boot Java backend (REST APIs, PDF generation, S3/SQS/SNS/KMS integration), a Scala.js fact-graph engine (declarative tax computation rules shared between JVM and JavaScript), a React/TypeScript frontend (Vite, USWDS, Redux, i18n), and supporting services for submission batching, status tracking, email notifications, and state tax authority integration. The fact-graph is the core innovation: a domain-specific declarative rule system using typed nodes (Dollar, Tin, Enum) and composable operators (Sum, Maximum, Switch, Placeholder) to encode the Internal Revenue Code as a knowledge graph that can be evaluated both server-side and client-side. The frontend uses a declarative flow configuration (JSX trees of Screen, Gate, CollectionLoop) driven by fact-graph state. The system integrates with MeF (Modernized e-File) for submission, SADI for identity verification, and a State API for exporting federal data to third-party state filing tools. The repository is archived and no longer maintained, so it represents a frozen snapshot of the 2024 tax season codebase with known deprecations and hardcoded constants.