Symbol Reference

Complete reference for all symbols used in EventFlow.

Symbol Quick Reference

Symbol	Position	Element	Example
(none)	-	Action (default)	order moves to #paid
?	line prefix	Guard	? cart is valid
??	line prefix	Guard (OR)	?? user is admin
=	line prefix	Assertion	= order is in #processing
>	after on	API Event	on> :checkout from @customer
@	inline	Actor	@customer
:	inline	Event	:checkout
#	inline	State	#processing
$	inline	Context	$total

Line Prefixes

Line prefixes indicate what the line does.

No Prefix (Action)

Lines without prefix are actions - the default line type:

order moves to #paid
emit :notification to @customer
$total increases by 100
send confirmation email

? (Guard)

Condition that must be true for indented actions:

? cart is not empty
  order moves to #checkout

Multiple guards are AND:

? cart is not empty
? user is logged in
  order moves to #checkout

?? (OR Guard)

Alternative condition - any one passing is enough:

? user is admin
?? user has override permission
  allow action

= (Assertion)

Verification statement in expect: blocks:

expect:
  = order is in #paid
  = $total equals 1200

> (API Event)

After on to mark public/external events:

on> :checkout from @customer
  // Externally accessible

Inline Symbols

Inline symbols indicate references within a line.

@ (Actor)

Reference to a machine/actor:

machine: @order
on> :checkout from @customer
emit :request to @payment

: (Event)

Reference to an event:

on> :checkout from @customer
emit :payment_request to @payment
on :payment_success from @payment

# (State)

Reference to a machine state:

order moves to #pending
? order is in #paid
order transitions to #completed

$ (Context Variable)

Reference to context data:

$total becomes 100
$items adds "Laptop"
? $total > 0

With type annotation:

$total: number becomes 100
$items: array adds "Laptop"

Case Rules

Element	Case	Example
Keywords	lowercase	machine:, scenario:, expect:
Actors	lowercase	@customer, @admin
States	lowercase	#checkout, #processing
Events	lowercase	:checkout, :payment_request
Context	lowercase	$total, $items
Types	lowercase	string, number, array
String literals	as-is	"Proceed to Checkout"

Type Annotations

Optional types for context variables:

Type	Description	Example
string	Text values	$name: string becomes "John"
number	Integers and decimals	$total: number becomes 100
boolean	True/false	$active: boolean becomes true
array	List of items	$items: array becomes empty
object	Key-value pairs	$config: object becomes empty

Comparison Operators

Used in guards and assertions:

Operator	Meaning	Example
equals / is	Equal to	? $total equals 100
is not	Not equal to	? $status is not "cancelled"
is greater than	>	? $total is greater than 100
is less than	<	? $count is less than 5
is at least	>=	? $age is at least 18
is at most	<=	? $items is at most 10
contains	Has element	? $items contains "Laptop"
is empty	Empty collection	? $cart is empty
is not empty	Has elements	? $items is not empty

State Transition Verbs

All equivalent - use what reads best:

Verb	Example
moves to	order moves to #paid
transitions to	order transitions to #approved
enters	payment enters #processing
becomes	ticket becomes #closed
changes to	status changes to #active

Guard Logic

AND Logic (multiple ?)

? condition1
? condition2
  // Runs only if BOTH true

OR Logic (??)

? condition1
?? condition2
  // Runs if EITHER true

Combined

? conditionA
? conditionB
?? conditionC
  // Runs if (A AND B) OR C

Default Case

? condition1
  handle case 1
? condition2
  handle case 2
otherwise
  handle default

// Or with empty ?
? condition
  handle condition
?
  handle else