# Part II — Thinking and Writing in Flows

> Learn Flow-Like FlowScript from nodes and document syntax through types, expressions, control flow, state, functions, events, interfaces, and complete Apps.

- **Document type:** Part overview
- **Canonical HTML:** [https://book.flow-like.com/part-2/](https://book.flow-like.com/part-2/)
- **Markdown alternate:** [https://book.flow-like.com/part-2/index.md](https://book.flow-like.com/part-2/index.md)
- **Book:** FlowBook — The FlowScript Book
- **Edition:** Open edition · 2026
- **Publisher:** Flow-Like
- **Language:** en
- **Topics:** Flow-Like FlowScript guide, workflow execution, FlowScript types, FlowScript control flow, Flow-Like Apps
- **LLM index:** [https://book.flow-like.com/llms.txt](https://book.flow-like.com/llms.txt)

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Part II is the working language guide. It teaches FlowScript through the graph and runtime model
the language represents, so familiar-looking syntax never becomes a second, hidden execution
engine.

The path starts with nodes, pins, wires, and the separation between data flow and execution
flow. From there it opens a complete FlowScript document, builds typed values and interfaces,
and shows how catalog calls become visible nodes. Later chapters make expressions, branches,
loops, state, functions, caching, Events, pages, schedules, and REST boundaries explicit.

By the end of this part, you will be able to:

- read the canonical structure of a FlowScript file;
- connect types, expressions, and calls to their visible graph representation;
- reason about sequence, branching, repetition, parallelism, stopping, and return;
- place configuration, secrets, cache data, and durable state in the right trust boundary;
- extract repeated graph logic into typed functions and safe caches; and
- expose one Flow through an interactive page, Quick Action, schedule, or authenticated API.

Read these chapters in order for the full progression, or use the chapter descriptions below to
enter at the concept you need. Every chapter keeps returning to the same test: what does this
source mean on the Board, and what evidence does it leave when it runs or fails?

---

## Chapters in this part

- [Chapter 5: Nodes, Pins, Wires, and Execution](https://book.flow-like.com/part-2/05-nodes-pins-wires-execution/index.md): Learn how Flow-Like separates typed data flow from execution order, evaluates pure nodes on demand, and represents sequence, parallelism, and layers.
- [Chapter 6: Anatomy of a FlowScript Document](https://book.flow-like.com/part-2/06-anatomy-of-a-flowscript-document/index.md): Read a canonical Flow-Like FlowScript file from use declarations and interfaces through variables, functions, events, identity anchors, and diagnostics.
- [Chapter 7: Values, Types, Collections, and Interfaces](https://book.flow-like.com/part-2/07-values-types-collections-interfaces/index.md): Learn how FlowScript types map to visible pins, including scalars, arrays, maps, sets, structs, interfaces, schema propagation, and type diagnostics.
- [Chapter 8: Calling the Node Library](https://book.flow-like.com/part-2/08-calling-the-node-library/index.md): Discover and call Flow-Like catalog nodes with qualified names, imports, method syntax, named output pins, generated declarations, and typed search.
- [Chapter 9: Expressions, Operators, and Readable Sugar](https://book.flow-like.com/part-2/09-expressions-operators-readable-sugar/index.md): See how FlowScript operators, ternaries, template literals, and struct field access lower to visible catalog nodes without hiding configuration or data flow.
- [Chapter 10: Branches, Loops, Parallelism, and Return](https://book.flow-like.com/part-2/10-branches-loops-parallelism-return/index.md): Build visible control flow with if branches, named execution arms, sequential and parallel loops, bounded while, stopping, and return boundaries.
- [Chapter 11: State, Configuration, Runtime Values, and Secrets](https://book.flow-like.com/part-2/11-state-configuration-runtime-values-secrets/index.md): Choose the right scope and trust boundary for local bindings, Flow variables, runtime configuration, BYOK secrets, cache data, files, and durable state.
- [Chapter 12: Functions, Layers, Handlers, and Caching](https://book.flow-like.com/part-2/12-functions-layers-handlers-caching/index.md): Turn repeated node graphs into reusable typed functions, distinguish layers from handlers and Events, and design safe cache keys and invalidation.
- [Chapter 13: Events, Interfaces, and Complete Apps](https://book.flow-like.com/part-2/13-events-interfaces-complete-apps/index.md): Expose one typed Flow through an interactive Page, Quick Action, Cron schedule, and authenticated REST API with explicit identity, versions, and evidence.