Cookbook

Short, focused recipes for the things you actually do. Each recipe is self-contained — copy it into your project as a starting point.

Looking for longer guided builds? See Tutorials.

Getting data in

• Read a file, line by line — BufReader, async variants, write safely.
• Parse JSON into typed records — compile-time-validated JSON literals, @derive(Deserialize), interpolated json#"""...""", dynamic Data access.
• Validate at boundaries — refinement types at system edges; typed error responses.
• Regular expressions — compile-time- validated rx#"..." literals, capture groups, anchoring.

Talking to the world

• HTTP client — typed responses, retries, TLS config.
• HTTP server — minimal typed server with routing, context-based DI, and test mocks.
• TCP sockets — echo server, framing, half-close handling.
• DNS lookups — A/AAAA records, SRV, MX, timeouts.

Running code

• Async basics — spawn, .await, select, cancellation.
• Channels — MPSC, broadcast, one-shot with back-pressure.
• Generators — sync fn* and async async fn* iterators.
• Structured concurrency with nursery — parallel fetch, bounded parallelism, cancellation semantics.
• Resilience — retries, circuit breakers, supervision policies.
• Scheduler — intervals, cron-like triggers, priority queues.

Collections & state

• Collections idioms — grouping, counting, sorting, Map.entry patterns.
• Interior mutability — Cell / RefCell / OnceCell / LazyCell decision tree.
• Sharing state across tasks — Shared<Mutex<T>>, avoiding deadlocks, atomic alternatives.
• Shared ownership — Shared<T> vs Rc<T>, breaking cycles with Weak<T>.

Types that prove things

• Refinement patterns — positive / nonzero / in-range, length-indexed collections, pattern-validated text, cross-parameter refinements.
• Shape-safe tensors — Tensor<T, Shape> with compile-time matmul / conv shape checks.
• calc proofs — equational reasoning inside a function body.
• Adding @verify(formal) — promoting runtime checks into SMT-proven invariants.
• @logic functions — extending the solver's vocabulary soundly.
• Debugging SMT failures — counter- example diagnostics, timeouts, strategy escalation.

Memory

• References in practice — when to use &T vs &checked T vs &unsafe T.
• Arenas — GenerationalArena<T>, bulk free, parser trees.

Metaprogramming

• Writing a @derive(...) — a full walk-through of @derive(DisplayAll) with verum expand-macros.

Systems

• CLI tool — argument parsing, subcommands, config files, coloured errors, exit codes.
• TUI with the Elm loop — 7-layer terminal framework, scenes, event handling.
• FFI — calling C libraries, boundary contracts, ownership transfer.

See also

• Tutorials — longer end-to-end builds for a URL shortener, parser combinator, verified data structure, ETL pipeline, and MNIST classifier.
• Guides — FAQ, performance, security, troubleshooting.