Package	`@formscript/types`
Specification	5, 5.2, 5.3, 5.5
Depends on	`ast`

`@formscript/types`

The type system of §5 of the specification: the lattice, the coercion table, the absence model and the field state.

The lattice

import { isAssignable, isSubtype, join, scalar } from '@formscript/types';

isSubtype(scalar('integer'), scalar('number'));   // true
isAssignable(scalar('any'), scalar('boolean'));   // true — `any` fits anywhere
join(scalar('string'), scalar('number'));          // `any`

The lattice is deliberately small. string is a subtype of display; no other type is a subtype of any other, and display is not a subtype of string.

Four conversions are permitted (§5.3) — string → number, string → date, number → integer, integer → number. Everything else is an error. canCoerce answers the question; coerce performs the conversion and returns a failure rather than throwing.

Absence

null and inapplicable are distinct first-class values (§5.5), and neither is the same thing as "empty":

import { UNKNOWN, INAPPLICABLE, isAbsent, isEmpty } from '@formscript/types';

isEmpty is about content — an empty string is empty. isAbsent is about absence — an unknown or inapplicable value is absent.

Field state

A field's state has three axes (§5.2): content, applicability and validity. deriveValidity folds the constraint outcomes into it, and satisfiesRequired answers the question the required constraint asks.

Public API

42 exported symbols.

Absence type

ANY re-export

Applicability type

arrayOf re-export

canCoerce function

Whether the conversion is one of the four permitted coercions.

coerce function

Performs a coercion. A coercion that fails yields the error value rather than throwing (Spec-5.18) — the caller receives `ok: false` and raises `E-EVAL-06` /…

Coercion interface

CoercionKind type

The permitted coercions are exactly four (Spec-5.16).

CoercionResult type

COERCIONS const

ConstraintOutcome interface

Content type

contentOf function

The content of a field holding `value` (Spec-5.4).

DEFAULT_REPEAT_MAX const

The default maximum number of rows in a `repeat` that declares no `max` (Spec-7.9). A repeat's `max` is the iteration bound the cost model uses (Spec-6.6), s…

DEFERRED const

deriveValidity function

Derives a field's validity from its three stored axes and its constraint outcomes (Spec-5.2). Validity is never stored.

describeState function

describeType re-export

dominantAbsence function

`inapplicable` dominates `null` when the two meet (Spec-5.18).

FAILED const

FieldState interface

INAPPLICABLE const

INITIAL_STATE const

isAbsent function

isAssignable re-export

isEmpty function

Whether a value is `empty` (Spec-5.4): `null`, a zero-length string, an empty array, or an empty choice. `0` and `false` are **not** empty.

isInapplicable function

isSubtype re-export

isUnknown function

join re-export

mayShowViolation function

Whether a violation may be shown yet (Spec-5.7).

PASSED const

readValue function

The value an expression sees when it reads a field (Spec-5.8).

satisfiesRequired function

A field's declared type participates in the empty check for `required`.

scalar re-export

TypeBound interface

TypeDescriptor interface

TypeName type

typeOfLiteral re-export

typeRefToDescriptor re-export

UNKNOWN const

The two absence values (Spec-5.22). `null` means *unknown*; `inapplicable` means *not applicable*. They are distinct first-class values and neither equals an…

Validity type