Quick Reference

A quick reference guide to Turn's core primitives, syntax grammar, expressions, and built-in tools.

Core Primitives

⬡turn

First-class unit of behavior. turn { ... } defines a control cycle representing one step of agent execution. Closures are turn(args) -> Type { ... }.

⬡context.append

Bounded working context managed by the runtime. The language enforces |context| ≤ N to prevent unbounded lists.

⬡remember / recall

Persistent process memory as a primitive store. remember(key, value) writes; recall(key) reads. Returns null when key is missing.

⬡call

External effects suspend execution and resume with a value. call(tool_name, arg) serves as the single suspension boundary enabling deterministic replay.

⬡infer

Probabilistic effect returning a typed value. infer Type { prompt } invokes an LLM with cognitive type safety where the runtime validates the schema.

⬡suspend

Explicit durable checkpoint. suspend; writes the entire VM state to disk for orthogonal persistence.

⬡spawn

Actor-style concurrency. spawn turn() { ... } creates an isolated process with its own state and mailbox.

Expressions & Statements

Literals: 42, "hello", true, false, null, [1, 2, 3], { key: val }
Variables: let id = expr;
Operators: +, ==, !=, <, >, <=, >=, and, or, !
Indexing: expr[index] for lists and maps
Member access: expr.field for structs and maps
Control flow: if expr { ... } else { ... }, while expr { ... }
Structs: struct Name { field: Type, ... };

Built-in Tools (Alpha)

Tool	Purpose
`echo(val)`	Returns the value (prints to stdout)
`sleep(seconds)`	Pauses execution
`http_get(url)`	GET request
`http_post({url, body})`	POST with JSON body
`json_parse(str)`	Parse JSON string to Value
`json_stringify(val)`	Value to JSON string
`fs_read_blob(path)`	Returns a Blob resolving the MIME-type
`load_driver(path)`	Maps driver configurations into env vars
`env_set(key, val)`	Sets an environment variable
`sys_exec({bin, ...args})`	Native CLI execution (keys mapped to string args)

Next Steps

Types and Errors Every type in Turn and the monadic error model.
Error Handling Monadic error routing with Result and Option.