Language Reference¶

Concise reference for Mora's type system, verbs, operators, and built-in functions. For the full relation catalog — every relation, its signature, type, legal verbs, and source — see relations.md, which is auto-generated from data/relations/**/*.yaml and always reflects the shipping set.

For a tutorial introduction, see the Language Guide.

Argument types¶

Every relation argument has one of these types:

Type	Description
`Int`	32-bit signed integer
`Float`	IEEE-754 single-precision
`String`	UTF-8 (stored as `BSFixedString` at runtime)
`FormRef`	A record FormID (compile-time `@EditorID`)
`RefId`	A placed-reference FormID (live instance)
`Keyword`	Interned symbol (user-defined `:tag` value)

FormRef refers to a base record (a WEAP, NPC_, KYWD, …). RefId refers to a placed reference — an instance of a base record in the world. The only way from a RefId to its FormRef is the explicit bridge ref/base_form(R, F).

Type constructors and verbs¶

Every relation is declared with a type of the form ctor<Elem>. The constructor determines which verbs are legal in head (effect) position.

Constructor	Legal verbs in head	Example
`scalar<T>`	`set`	`=> set form/name(F, "Nazeem")`
`countable<T>`	`set`, `add`, `sub`	`=> add player/gold(P, 100)`
`list<T>`	`add`, `remove`	`=> add form/keyword(W, @Enchanted)`
`const<T>`	(none — read-only)	`ref/health(R, H)` in body only
`predicate`	(none — unary existence)	`form/npc(F)`

Verb/shape mismatches are compile errors pointing at the offending line.

Effect syntax¶

=> <verb> <namespace>/<name>(<args>)

Examples:

=> set form/damage(W, 20)
=> add form/keyword(W, @Enchanted)
=> remove form/keyword(W, @Cursed)
=> sub player/gold(P, 10)
=> add player/notification(P, "You found a bandit.")

Comparison operators¶

Operator	Meaning
`==`	Equal
`!=`	Not equal
`<`	Less than
`<=`	Less than or equal
`>`	Greater than
`>=`	Greater than or equal

Comparisons don't bind variables — their operands must already be bound by earlier clauses.

Arithmetic¶

Operator	Meaning
`+`	Addition
`-`	Subtraction
`*`	Multiplication
`/`	Division

Standard precedence: * and / bind tighter than + and -. Expressions widen to Float if any operand is a float.

Built-in functions¶

Function	Arity	Description
`max(a, b)`	2	Larger of two numeric values
`min(a, b)`	2	Smaller of two numeric values
`abs(x)`	1	Absolute value
`clamp(x,l,h)`	3	Clamp `x` to `[l, h]`

All are pure and deterministic. Unknown name or wrong arity is a hard compile-time error. Result types widen to Float when any argument is a float, otherwise stay Int.

Rule annotations¶

Annotation	Meaning
(none)	Static. Body uses only compile-time-known relations.
`maintain`	Differential truth maintenance; auto-retracts on `-1`.
`on`	Edge-triggered; fires once on `+1`, no retraction.

The phase classifier validates annotations against the rule body:

Unannotated rule using any dynamic relation → error, "did you mean maintain or on?"
maintain rule using event/* → error (events are edge-shaped, not state).
maintain rule whose head uses an effect without a retract handler → error.

Identifier literals¶

Syntax	Meaning
`@WeapMaterialIron`	EditorID reference; resolved to a FormID at compile time
`:high`, `:fire`	Keyword (interned symbol)
`42`, `1.5`	Int / Float literal
`"Nazeem"`	String literal (double-quoted, UTF-8)
`W`, `Base`	Logic variable (Capitalized identifier)