Expression Language

Expressions are strings. Non-string primitives (42, true, [], {}) are treated as literals.

Scopes

Scope	Available in	Description
`event.<field>`	actions, projections (derive), listeners	Event payload field
`event.ts`	all	Event timestamp (epoch ms) — reserved
`event.entity_id`	all	Routing entity ID — reserved
`event.type`	all	Event type string — reserved
`entity.<field>`	actions (core/side_effects), preflight	Current entity state (dot notation)
`input.<field>`	actions (`entity_id_expr`), queries	Action input or query parameter
`intent.<field>`	actions	Alias for `input.<field>`
`state.id`	actions	Current entity ID
`resources.<type>["<id>"].<field>`	all	Static resource lookup
`it.<field>`	`find`, `filter`, `remove`, `for_each`	Iterator variable
`item.<field>`	`emit_each`, `for_each`	Iterator variable
`<var>.<field>`	after `find … as: var` or `clone … as: var`	Bound variable
`project.<field>`	actions	Platform-level shared state
`global.<field>`	actions	Global read-only state

event.<field> in rules vs projections

In rules: event.amount reads from the intent payload directly. In projection derive:: event.amount and event.payload.amount are both accepted (the latter is a backwards-compat alias).

Never use event.payload.amount in rules — it always returns null.

Operators

==  !=  >  <  >=  <=  &&  ||
+   -   *   /
!expr              (logical not: !contains(entity.tags, "x"))
cond ? a : b       (ternary)
val ?: default     (null-coalesce)
entity['path']     (bracket access)
array[0]           (index access)

Built-in functions

Function	Description
`size(array)`	Array length
`sum(array)`	Sum of numeric values
`contains(array, value)`	Check if array contains value
`map(array, expr)`	Transform array
`filter(array, expr)`	Filter array (keep matching)
`max(a, b)`	Maximum of two values
`min(a, b)`	Minimum of two values
`floor(value)`	Floor of a number
`concat(a, b, …)`	Concatenate strings
`join(array, sep)`	Join array to string
`format_date(ts)`	Format epoch ms timestamp
`is_prev_day(d1, d2)`	Check if two timestamps are on different days
`shard(expr, N)`	Map expression to shard ID 0..N-1
`lookup(stream, id_expr).<field>`	Cross-entity lookup (projections only)
`LOOKUP_FIELD('stream', id, '/path')`	Cross-stream field read (rule expressions / preflight)

FORBIDDEN expressions

The following are rejected at compile time with VERR_NON_DETERMINISTIC_EXPRESSION or VERR_SPEL_FORBIDDEN_FUNCTION:

now()       random()    uuid()      Math.random
shuffle()   nanoTime()  System.*    Runtime.*
Process.*   Thread.*    Runnable.*  getClass
forName     eval        exec
http.*      redis.*     db.*        kafka.*
s3.*        stripe.*    env.*       secret.*

All IDs must be deterministic. Build them with concat:

value: "concat('notif_', event.user_id, '_', event.show_id)"

commit_envelopes Rule Execution