Keyword Reference

Every identifier in this table is reserved — you cannot use it as a variable, function, or type name. The table is generated from the lexer source of truth (crates/zolo-lexer/src/keywords.rs). Links point to the by-example chapter that covers each keyword in depth; "—" means the keyword is reserved for a future language feature that has no chapter yet.

Keyword	Meaning	Chapter
after	Schedules a block to run once after a duration (temporal).	Temporal
as	Casts or renames a value in a pattern, import, or type expression.	Modules
async	Marks a function as asynchronous; the body returns a future.	Concurrency
await	Suspends the current async function until a future resolves.	Concurrency
break	Exits the innermost loop immediately.	Control Flow
catch	Handles an exception thrown inside a try block.	Error Handling
comptime	Evaluates an expression at compile time.	Comptime
const	Declares a compile-time constant binding.	Variables
const_assert	Asserts a condition at compile time; fails the build if false.	Comptime
continue	Skips the rest of the current loop iteration.	Control Flow
defer	Runs a block when the enclosing scope exits (success or failure).	Control Flow
defer_err	Runs a block only when the enclosing scope exits with an error.	Error Handling
defer_ok	Runs a block only when the enclosing scope exits successfully.	Error Handling
effect	Declares an algebraic effect interface.	Effects
else	Provides an alternative branch for an if expression.	Control Flow
enable	Enables an optional language or compiler feature (directive).	Directives
enum	Defines a sum type with named variants.	Data Structures
every	Schedules a block to run repeatedly on an interval (temporal).	Temporal
false	Boolean literal false.	Primitives and Numbers
finally	Runs a block unconditionally after a try/catch sequence.	Error Handling
fn	Declares a function.	Functions
for	Iterates over an iterable value.	Control Flow
guard	Early-returns from a function if a condition is not met.	Control Flow
handle	Provides an implementation for an algebraic effect.	Effects
if	Introduces a conditional expression.	Control Flow
impl	Implements methods or a trait for a type.	OOP
in	Separates the loop variable from the iterable in a for loop.	Control Flow
is	Tests whether a value matches a type or variant pattern.	Pattern Matching
let	Declares an immutable local binding.	Variables
loop	Introduces an infinite loop (must be exited with break).	Control Flow
machine	Declares a state machine type.	State Machines
macro	Declares a macro definition.	Macros
match	Pattern-matches a value against a set of arms.	Control Flow
mod	Declares or references a module.	Modules
mut	Makes a binding or field mutable.	Variables
newtype	Declares a newtype wrapper around an existing type.	Data Structures
nil	The null / absent value literal.	Primitives and Numbers
on	Attaches a lifecycle hook or event handler to a scope.	Lifecycle Hooks
override	Overrides a compiler setting or default behavior (directive).	Directives
perform	Invokes an algebraic effect operation.	Effects
pub	Makes a declaration visible outside its module.	Modules
requires	Declares a compile-time requirement or dependency (directive).	Directives
return	Returns a value from a function early.	Functions
schema	Declares a data-validation schema.	Schemas
scope	Creates an explicit concurrent scope that waits for all tasks.	Concurrency
select	Waits on the first of several concurrent channels or futures.	Concurrency
self	Refers to the current instance inside an impl block.	OOP
sleep	Pauses execution for a duration (temporal).	Temporal
spawn	Launches a concurrent task.	Concurrency
struct	Declares a product type with named fields.	Data Structures
timeout	Cancels an operation if it does not complete within a duration.	Temporal
trait	Declares a set of methods that a type must implement.	OOP
true	Boolean literal true.	Primitives and Numbers
try	Wraps a block to intercept thrown errors.	Error Handling
type	Declares a type alias.	Data Structures
use	Imports names from a module or plugin into the current scope.	Modules
using	Embeds the fields and methods of a struct field into the parent type.	Data Structures
var	Declares a mutable local binding (shorthand for let mut).	Variables
where	Attaches trait bounds to a generic parameter list.	OOP
while	Loops while a condition holds.	Control Flow
with	Pairs a handle block with the effect scope it covers.	Effects
yield	Produces a value from a generator function.	—