Validation & Results

Validation & Results

FsFlow provides a unified stack for handling failure, ranging from pure predicate checks to complex, path-aware diagnostics graphs.

The core philosophy is to check once, lift later. You write your pure logic using simple tools and then lift them into richer execution contexts (like Flow or Flow) only when needed.

The Progression

1. Pure Checks: Build reusable predicates with the Check module.
2. Result & Validation: Domain logic that either fails fast (result {}) or accumulates multiple errors (validate {}).
3. Guard: The bridge that allows pure checks and simple sources to fail a flow with a specific domain error.
4. Flow: The application boundary where you need dependencies, async work, or interop.

Why use this stack?

• Consistency: Use the same patterns for simple form validation and complex background job logic.
• Testability: Pure checks are trivial to test in isolation.
• Ergonomics: Computation expressions like result {} and validate {} make complex logic readable and idiomatic.
• Structured Reporting: Diagnostics graphs preserve the shape of your data, making it easy to report errors back to users or external systems.

Getting Started

If you are new to FsFlow, start with Pure Checks to see how the smallest building blocks work.

See it in Action

For a complete, runnable example that demonstrates how these pieces fit together—from nested validation to JSON API error formatting—see the Diagnostics Example.