Keywords

This page lists every reserved keyword in the Tova language in alphabetical order. Each entry includes a brief description and a minimal code example.

Reserved Keywords

Keyword	Description
and	Logical AND (keyword form)
as	Alias in imports
async	Mark a function as asynchronous
await	Wait for an async result
break	Exit a loop early
browser	Define a browser block
catch	Handle errors from a try block
client	Deprecated alias for browser
component	Declare a reactive UI component
computed	Declare a derived reactive value
continue	Skip to the next loop iteration
defer	Schedule code to run at scope exit
derive	Auto-derive trait implementations for a type
effect	Declare a reactive side effect
elif	Chained conditional branch
else	Fallback conditional branch
export	Reserved keyword (use pub instead)
extern	Declare an external (foreign) binding
false	Boolean false literal
field	Declare a form field inside a form block
finally	Code that always runs after try/catch
fn	Declare a function
for	Iterate over a collection or range
form	Declare a reactive form inside a browser/component scope
from	Specify the module source in an import; receive from a channel in select
group	Declare a field group inside a form block
guard	Assert a condition or execute an else block
if	Conditional branch
impl	Implement methods or traits for a type
import	Bring names from another module into scope
in	Membership test; iteration target in for loops
interface	Define a structural type contract
is	Type-checking operator
let	Reserved (hard error — destructure directly without a keyword)
loop	Infinite loop
match	Pattern matching expression
mut	Reserved (use var instead)
nil	The absence-of-value literal
not	Logical NOT (keyword form)
or	Logical OR (keyword form)
pub	Mark a declaration as public
return	Explicit early return from a function
route	Define an HTTP route in a server block
server	Define a server-side block
shared	Define a block shared between server and browser
state	Declare a reactive state variable
steps	Declare wizard steps inside a form block
store	Declare a reactive store
trait	Define a named set of behaviors
true	Boolean true literal
try	Begin an error-handling block
type	Declare a custom type (struct or ADT)
var	Declare a mutable variable
when	Guard condition in for loops
while	Loop while a condition is true
with	Resource management with cleanup
yield	Yield a value from a generator

INFO

Several identifiers that appear keyword-like are actually contextual identifiers -- they are NOT reserved by the lexer and can be used as variable names outside their respective contexts. See Contextual Identifiers and Data Block Identifiers below.

Contextual Keywords (HTTP Methods)

These identifiers are recognized only within server blocks for route declarations. They are parsed as regular identifiers, not as keyword tokens:

Keyword	Description
GET	HTTP GET method
POST	HTTP POST method
PUT	HTTP PUT method
DELETE	HTTP DELETE method
PATCH	HTTP PATCH method
HEAD	HTTP HEAD method
OPTIONS	HTTP OPTIONS method

Contextual Identifiers (Block Keywords)

The following identifiers are NOT reserved keywords. They are detected contextually by the plugin system at the top level only and can be used as variable names in other contexts:

Identifier	Description
test	Define a test block
bench	Define a benchmark block
security	Define a security policy block
cli	Define a CLI tool block
edge	Define an edge/serverless block
concurrent	Define a structured concurrency block
deploy	Define a deployment configuration block
theme	Define a design token theme block
data	Define a data block for sources, pipelines, and validation

Contextual Identifiers (Concurrency)

These identifiers are recognized only within concurrent blocks or as prefix operators in concurrent contexts:

Identifier	Description
spawn	Launch a concurrent task inside a concurrent block
select	Multiplex across channel operations

Contextual Identifiers (Data Block)

These identifiers are recognized only inside data blocks:

Identifier	Description
ai	Declare an AI provider configuration (inside server blocks)
pipeline	Declare a named transform chain in a data block
source	Declare a data source in a data block
validate	Declare validation rules for a type in a data block
refresh	Set a refresh policy for a data source

Contextual Identifiers (Styling)

Identifier	Description
style	Define a scoped CSS style block (consumed as a STYLE_BLOCK token by the lexer)

---

Keyword Details

ai

Declares an AI provider configuration inside a server block. Can be unnamed (default) or named for multiple providers.

server {
  ai {
    provider: "anthropic"
    model: "claude-sonnet-4-20250514"
    api_key: env("ANTHROPIC_API_KEY")
  }

  ai "gpt" {
    provider: "openai"
    model: "gpt-4o"
    api_key: env("OPENAI_API_KEY")
  }

  answer = ai.ask("Hello")
  other = gpt.ask("Hello")
}

and

Logical AND operator. Short-circuits: the right operand is not evaluated if the left is falsy.

if is_valid and is_active {
  process()
}

as

Renames an import to a local alias.

import { readFile as read } from "fs"

async

Marks a function as asynchronous. An async function returns a Promise.

async fn fetch_data(url) {
  response = await fetch(url)
  await response.json()
}

await

Suspends execution until an asynchronous value resolves.

async fn main() {
  data = await fetch_data("/api/users")
}

main()

bench

Defines a benchmark block inside a test file. Used to measure execution time of a code snippet.

bench "array sorting" {
  data = range(1000) |> shuffle()
  sorted(data)
}

break

Exits the nearest enclosing for or while loop immediately.

for item in items {
  if item == target {
    break
  }
}

catch

Handles errors thrown in a try block. The caught error is bound to an optional variable.

try {
  data = parse(input)
} catch err {
  log("Parse error: {err}")
}

browser

Opens a browser block. Code inside is compiled only for the browser.

browser {
  state count = 0
  component Counter() {
    <button on:click={fn() count += 1}>{count}</button>
  }
}

component

Declares a reactive UI component that renders JSX.

component Greeting(name) {
  <h1>"Hello, {name}!"</h1>
}

computed

Declares a derived value that automatically updates when its dependencies change.

state items = []
computed total = len(items)

continue

Skips the remainder of the current loop iteration and proceeds to the next.

for i in 0..100 {
  if i % 2 == 0 {
    continue
  }
  print(i)
}

concurrent

Defines a structured concurrency block. All spawned tasks within the block must complete (or be cancelled) before execution continues past it. Supports mode modifiers: cancel_on_error, first, and timeout(ms).

concurrent {
    users = spawn fetch_users()
    posts = spawn fetch_posts()
}
// users and posts are Result values

concurrent cancel_on_error {
    a = spawn validate(input)
    b = spawn check_permissions(user)
}

concurrent timeout(5000) {
    data = spawn slow_operation()
}

See the Concurrency guide for full details.

data

Opens a data block for declaring sources, pipelines, validation rules, and refresh policies. The data {} block is a top-level block alongside shared, server, and browser.

data {
  source users = read("users.csv")
  pipeline active = users |> where(.active)
  validate User { .email |> contains("@") }
  refresh users every 15.minutes
}

defer

Schedules an expression to run when the enclosing scope exits, regardless of how it exits.

fn process_file(path) {
  file = open(path)
  defer close(file)
  read(file)
}

derive

Automatically generates trait implementations for a type.

type Point {
  x: Float
  y: Float
} derive [Eq, Show, JSON]

effect

Declares a reactive side effect that re-runs when its dependencies change.

state query = ""
effect {
  results = search(query)
  render(results)
}

elif

A chained conditional branch. elif is the idiomatic Tova style. else if is also accepted by the parser.

if score >= 90 {
  "A"
} elif score >= 80 {
  "B"
} elif score >= 70 {
  "C"
} else {
  "F"
}

else

The fallback branch of an if/elif chain or a for loop.

if condition {
  handle_true()
} else {
  handle_false()
}

export

Reserved keyword. Use pub to make declarations accessible to other modules.

extern

Declares an external binding provided by the host environment.

extern fn console_log(msg)

false

The boolean false literal.

is_done = false

field

Declares a form field inside a form block. Each field gets reactive value, error, and touched signals with optional validators.

form login {
  field email: String = "" {
    required("Email is required")
    email("Must be valid")
  }
}

See Form Block for full documentation.

finally

Specifies a block that always executes after try/catch, whether or not an error occurred.

try {
  data = load()
} catch err {
  log(err)
} finally {
  cleanup()
}

fn

Declares a named function or an anonymous lambda. Together with the arrow form (x => expr), fn is one of the two canonical function forms in Tova — there is no function, lambda, or def keyword.

fn add(a, b) {
  a + b
}

double = fn(x) x * 2          // anonymous fn
doubled = nums.map(x => x * 2)  // arrow form — prefer for short inline callbacks

See Functions › The Two Canonical Forms for when to pick which.

for

Iterates over a range or collection. Supports an optional second variable for key/index.

for item in items {
  print(item)
}

for i, val in items {
  print("{i}: {val}")
}

form

Declares a reactive form controller inside a browser {} or component scope. Supports fields, groups, arrays, wizard steps, and built-in validators.

form checkout {
  field email: String = "" { required("Required") }
  group shipping {
    field street: String = "" { required("Required") }
  }
  on submit { server.placeOrder(checkout.values) }
}

See Form Block for full documentation.

from

Specifies the module path in an import statement.

import { sqrt, PI } from "math"

group

Declares a field group inside a form block. Groups namespace related fields and support conditional visibility with when.

form checkout {
  group shipping {
    field street: String = "" { required("Required") }
    field city: String = "" { required("Required") }
  }
  group billing {
    field sameAsShipping: Bool = true
    group address when !sameAsShipping {
      field street: String = "" { required("Required") }
    }
  }
}

See Form Block for full documentation.

guard

Asserts a condition. If the condition is false, the else block executes (typically returning or breaking).

fn process(input) {
  guard input != nil else {
    return Err("input is nil")
  }
  // continue with valid input
  Ok(transform(input))
}

if

Conditional branching. Can be used as a statement or an expression.

// As statement
if ready {
  start()
}

// As expression
label = if count == 1 { "item" } else { "items" }

is

Type-checking operator. Tests whether a value is of a given type or ADT variant at runtime. Can be negated with is not.

value = "hello"
value is String       // true
value is Int          // false
value is not Nil      // true

// Works with ADT variants
result = Ok(42)
result is Ok          // true
result is Err         // false

impl

Implements methods or trait conformance for a type.

impl Point {
  fn distance(self, other) {
    sqrt((self.x - other.x) ** 2 + (self.y - other.y) ** 2)
  }
}

import

Brings named exports from another module into the current scope.

import { map, filter, reduce } from "stdlib/collections"

in

Tests membership or specifies the iteration target in a for loop.

if "admin" in roles { grant_access() }

for x in 0..10 { print(x) }

interface

Defines a structural contract that types can implement.

interface Printable {
  fn toString(self) -> String
}

let

Reserved keyword that produces a compile-time hard error. Tova does not use let — destructure directly without any keyword:

// These will NOT compile (uncommenting the next lines raises hard diagnostics):
// let { name, email } = user
// let [first, ...rest] = items
// Diagnostic: 'let' is not valid in Tova. For destructuring, use { name, email } = user directly
// Diagnostic: 'let' is not valid in Tova. For destructuring, use [first, ...rest] = items directly

// Destructure directly (no keyword needed):
{ name, email } = user
[first, ...rest] = items
(x, y) = point

WARNING

let is a hard error in Tova with a helpful message directing you to destructure directly. Use x = value for simple bindings, var x = value for mutable variables, and { a, b } = obj / [a, b] = list / (a, b) = pair for destructuring.

loop

Creates an infinite loop that runs until explicitly terminated with break. Useful for polling, event loops, and retry patterns.

var attempts = 0
loop {
  result = try_connect()
  if result.isOk() {
    break
  }
  attempts += 1
  if attempts > 5 {
    break
  }
}

Labels work with loop for nested loop control:

outer: loop {
  inner: loop {
    if done {
      break outer
    }
  }
}

match

Pattern matching expression. Exhaustive by design.

match result {
  Ok(value) => print(value)
  Err(msg) => print("Error: {msg}")
}

mut

Reserved keyword that produces a compile-time error. Tova uses var for mutable variables instead.

// This will NOT compile (uncommenting the next line raises a hard diagnostic):
// mut x = 10
// Diagnostic: 'mut' is not supported in Tova. Use 'var' for mutable variables

// Use 'var' instead:
var x = 10
x = 20  // OK

nil

The absence-of-value literal, equivalent to JavaScript's null.

result = nil

not

Logical NOT operator (keyword form).

if not isEmpty(list) {
  process(list)
}

or

Logical OR operator. Short-circuits: the right operand is not evaluated if the left is truthy.

name = input or "default"

pipeline

Declares a named transform chain inside a data {} block. Pipelines can reference sources and other pipelines.

data {
  source users = read("users.csv")
  pipeline active = users |> where(.active)
  pipeline summary = active |> groupBy(.role) |> agg(count: count())
}

pub

Marks a declaration as publicly visible.

pub fn api_handler(req) {
  respond(200, "ok")
}

refresh

Sets a refresh policy for a data source inside a data {} block. Supports interval-based or on-demand refresh.

data {
  source rates = read("https://api.example.com/rates")
  refresh rates every 1.hour

  source orders = read("orders.csv")
  refresh orders on_demand
}

return

Explicitly returns a value from a function. Optional when the last expression is the return value.

fn find(items, target) {
  for item in items {
    if item == target {
      return item
    }
  }
  nil
}

route

Defines an HTTP route handler inside a server block.

server {
  route GET "/api/users" => {
    users = db.query("SELECT * FROM users")
    json(users)
  }
}

select

Multiplexes across multiple channel operations. Waits until one case is ready, then executes its body. Supports receive, send, timeout, and default cases.

select {
    msg from ch1     => print("Got: {msg}")
    ch2.send(value)  => print("Sent")
    timeout(5000)    => print("Timed out")
    _                => print("Nothing ready")
}

See the Concurrency guide for full details.

server

Opens a server-side block. Code inside is compiled only for the server.

server {
  db { url: "postgres://localhost/mydb" }
  route GET "/health" => "ok"
}

shared

Opens a block whose code is available on both server and client.

shared {
  type User {
    name: String
    email: String
  }
}

spawn

Launches a concurrent task inside a concurrent block. The spawned call returns Result<T, Error> -- success wraps in Ok, exceptions wrap in Err.

concurrent {
    result = spawn compute(data)
    spawn log_event("started")   // fire-and-forget
}

See the Concurrency guide for full details.

source

Declares a named data source inside a data {} block. Sources are lazily loaded and cached.

data {
  source users = read("users.csv")
  source config = read("config.json")
  source users: Table<User> = read("users.csv")  // with type annotation
}

state

Declares a reactive state variable in a browser block or component.

state count = 0
state name = "world"

store

Groups related reactive state, computed values, and methods.

store TodoStore {
  state items = []
  computed count = len(items)
  fn add(text) {
    items = [...items, {text: text, done: false}]
  }
}

steps

Declares wizard steps inside a form block. Each step references fields, groups, or arrays that must be valid before advancing.

form checkout {
  field email: String = "" { required("Required") }
  group shipping { /* ... */ }
  group payment { /* ... */ }

  steps {
    step "Account" { email }
    step "Shipping" { shipping }
    step "Payment" { payment }
  }
}

See Form Block for full documentation.

test

Defines a test block with a description string and body containing assertions. Tests are discovered and run by tova test.

test "addition works" {
  assertEq(1 + 1, 2)
}

test "string interpolation" {
  name = "world"
  assertEq("Hello, {name}!", "Hello, world!")
}

trait

Defines a named set of behavior (similar to a typeclass or protocol).

trait Comparable {
  fn compare(self, other) -> Int
}

true

The boolean true literal.

is_ready = true

try

Begins an error-handling block. Must be followed by catch and optionally finally.

try {
  data = parse(raw_input)
} catch err {
  data = default_value
}

type

Declares a custom type -- either a struct (product type) or an algebraic data type (sum type).

// Struct
type Point {
  x: Float
  y: Float
}

// ADT (sum type)
type Shape {
  Circle(radius: Float)
  Rectangle(width: Float, height: Float)
}

validate

Declares validation rules for a type inside a data {} block. Each rule is a column predicate.

data {
  validate User {
    .email |> contains("@"),
    .name |> len() > 0,
    .age >= 0
  }
}

var

Declares a mutable variable with an initial value.

var counter = 0
counter += 1

when

Guard condition in for loops. Filters elements before the loop body executes, acting as an inline filter.

for item in items when item.active {
  process(item)
}

// Equivalent to:
for item in items {
  if item.active {
    process(item)
  }
}

while

Loops while a condition is true.

var i = 0
while i < 10 {
  print(i)
  i += 1
}

with

Resource management statement. Opens a resource and guarantees cleanup when the block exits, similar to a try/finally pattern.

with open("data.txt") as file {
  content = file.read()
  process(content)
}
// file is automatically cleaned up here

yield

Yields a value from a generator function.

fn fibonacci() {
  var a = 0
  var b = 1
  while true {
    yield a
    a, b = b, a + b
  }
}

Non-Keywords

The following are not keywords in Tova, even though they might be expected from other languages:

Word	Status in Tova
throw	Not a keyword. Tova uses Result/Option for error handling.
class	Not a keyword. Use type for data types and impl for methods.
this	Not a keyword. Use self in impl blocks (passed explicitly).
else if	Accepted, but prefer elif for idiomatic Tova style.