RMT Reference: Conditions and Expressions

tools/rmt-language/vnext-parser.js is the source of truth for operators and operand forms.

Conditions appear after when and use a small declarative expression language.

Syntax

Operator	Form	Allowed contexts	Parameters	Function	Diagnostics	Related operators
when	when app.ready == true	Lifecycle, stream, event binding	condition expression	Enables work only when the condition passes.	Expression must be complete.	mount, on
&&	a == true && b == false	Condition	left and right expression	Logical AND.	Right side must be an expression.	`		`
`		`	`a == true		b == true`	Condition	left and right expression	Logical OR.	Right side must be an expression.	&&
!	!app.disabled	Condition	expression	Negates a boolean path or expression.	Argument must be an expression.	when
==	app.status == "ready"	Condition	two values	Equality comparison.	Both sides must parse.	!=
!=	app.status != "error"	Condition	two values	Inequality comparison.	Both sides must parse.	==
>	app.count > 0	Condition	two values	Greater-than comparison.	Both sides must parse.	>=
>=	app.count >= 1	Condition	two values	Greater-than-or-equal comparison.	Both sides must parse.	>
<	app.count < 10	Condition	two values	Less-than comparison.	Both sides must parse.	<=
<=	app.count <= 10	Condition	two values	Less-than-or-equal comparison.	Both sides must parse.	<
()	(app.ready == true)	Condition	expression	Groups logic.	Closing parenthesis is required.	&&, `		`
true	app.ready == true	Condition, primitive value	literal	Boolean true.	Function calls are not allowed.	false
false	app.disabled == false	Condition, primitive value	literal	Boolean false.	Function calls are not allowed.	true
null	app.value != null	Condition, primitive value	literal	Null value.	Literal only.	!=
Strings	"ready"	Condition, primitive value	quoted string	Static text value.	Strings need quotes.	contract, message
Integers	120	Condition, primitive value	integer	Numeric value.	Only integers are tokenized.	durationMs, weight
Paths	app.status.text	Condition, payload, reducer	qualified path	References state, input, detail, target or surface context.	Path must contain identifier segments.	payload, reduce

Allowed contexts

Conditions appear after when. Literals and paths also appear in primitive values, payload mappings and reducer expressions.

Parameters

Conditions allow paths, strings, integers, true, false, null, comparisons, !, &&, || and parentheses.

Description

The condition language is intentionally smaller than JavaScript. It allows decisions, but not function calls or free execution.

Examples

template reference.conditions {
  state app.ready type boolean initial true
  state app.disabled type boolean initial false
  state app.count type number initial 2
  portal app.root root "#app" layer surface

  surface shell kind page component x-section {
    portal app.root
    lane visible weight 80 {
      mount shell.card from endpoint app.card when (app.ready == true && !app.disabled) || app.count >= 1
    }
  }
}

Diagnostics

Function calls such as isReady() are not allowed and produce parser diagnostics. Missing parentheses or incomplete comparisons are also reported.

Related operators

when, mount, stream, on, payload, reduce.

Related reading

The RMT reference index shows which records accept conditions and expressions. Related article