Kumiki Specification

This is the normative specification of the Kumiki language and runtime. When the implementation in packages/ and this text disagree, this text wins, and the PR records which side gets fixed.

You do not have to read it end to end. Language Core is the one document to read before writing Kumiki; the rest answer a question you already have. Tutorials and how-tos are not specification and live in the guide, and every feature has a runnable file in examples.

Documents

Document	Contents
Language Core	the 7 layers (type / slot / effect / reducer / tile / fn / app) and expressions, statements, patterns
Standard Library	List / Map / Set / Option / Result / Time / domain types
Routing	patterns, parameters, route.enter / route.leave, redirects
Style	Style, layout, and themes
Forms	Forms, bind, validation
HTTP / Storage	HTTP / Storage effects and policies (latest / debounce / once …)
Lifecycle	Lifecycle, capabilities, error boundaries, suspense
Runtime	Runtime implementation guide (signal graph, mount, dispatch, dispose)
AI Editing	AI editing API, CRDT ops, referential integrity
Testing	Testing strategy
Error Codes	Error code catalog (E0000..E08xx)

Indexes

Three cross-references into the documents above, each generated from the compiler and the examples rather than written by hand.

Layer × feature matrix — where each feature touches the 7 layers

A cell links to the section that specifies that intersection; — means the dimension has no layer-specific rules there.

Feature	type	slot	effect	reducer	tile	fn	app
Language Core	§1.3	§1.4	§1.5	§1.6	§1.7	§1.8	§1.12
Standard Library	§2.1	—	§2.6	—	§2.3	§2.2 §2.4	§2.5
Routing	—	§3.2	§3.3.2	§3.4 §3.5	§3.3.1 §3.6	§3.3.3	§3.1
Style	—	—	—	—	§4.3 §4.4 §4.9	—	§4.2.2 §4.6
Forms	§5.1.2	§5.1	—	§5.4	§5.2 §5.3	§5.6	—
HTTP / Storage	§6.1.3 §6.1.4	§6.8	§6.1 §6.7	§6.2	—	—	§6.1.1
Lifecycle	—	§7.9	§7.6 §7.7	§7.1	§7.3 §7.4	—	§7.2 §7.5
Testing	—	§8.2.2	§8.5	§8.2	§8.4	§8.3	§8.6
AI Editing	—	—	—	§9.9	—	—	§9.2 §9.4
Runtime	—	§10.3	§10.4	§10.5	§10.3.4	—	§10.6 §10.9
Errors	E02xx	E01xx	E03xx	E06xx	E04xx E07xx	E03xx E08xx	E00xx

AI-editing CRDT ops (add / replace / remove / rename, §9.3.1) apply uniformly to definitions of every layer; the matrix row lists only the layer-specific sections.

Diagnostic codes — every code in Error Codes, by layer and feature

Code	Kind	Layer	Feature
E0000	parse-error	all	core
E0001	missing-404	app	routing
E0002	duplicate-timer-name	app	lifecycle
E0003	missing-app	app	core
E0004	duplicate-app	app	core
E0005	tile-cycle	tile	core
E0006	fn-cycle	fn	core
E0007	duplicate-definition	all	core
E0008	duplicate-clause / duplicate-key / duplicate-field / duplicate-param / duplicate-variant	all	core
E0009	type-cycle	type	core
E0102	undef-reducer	reducer	core
E0103	undef-ref / undef-slot	slot	core
E0104	undef-effect / init-not-effect-call	effect	core
E0106	undef-timer	reducer	lifecycle
E0105	undef-tile	tile	core
E0107	undef-motion	tile	style
E0108	undef-member	fn	stdlib
E0110	unknown-token-group	tile	style
E0109	test-wildcard-misuse	reducer	testing
E0111	orphan-sub-routes	tile	routing
E0112	duplicate-sub-route	tile	routing
E0113	sub-routes-without-outlet	tile	routing
E0114	sub-routes-without-wildcard-parent	tile	routing
E0115	reserved-slot-name	slot	core
E0116	undef-call	fn	core
E0117	undef-type	type	core
E0118	undef-theme	app	style
E0119	route-bind-out-of-scope	reducer	routing
E0120	route-in-app-init	app	routing
E0121	reserved-bind-name	reducer	core
E0122	duplicate-pattern-bind	reducer	core
E0123	duplicate-effect-bind	reducer	core
E0124	type-constructor-qualifier	type	core
E0127	fn-as-value	all	core
E0128	value-as-child	tile	core
E0129	unrendered-arg	tile	core
E0201	type-mismatch	type	core
E0202	emit-arg-type-mismatch	reducer	core
E0204	effect-id-misuse	effect	http
E0205	bind-on-file-input	tile	forms
E0206	file-only-prop	tile	forms
E0207	pat-arity-mismatch	type	core
E0208	pat-type-mismatch	type	core
E0209	pat-unknown-variant	type	core
E0210	type-arity-mismatch	type	core
E0211	undef-tile-in-selector	reducer	core
E0212	selector-id-mismatch	reducer	core
W0212	ui-event-tile-mismatch	reducer	core
E0213	call-arity-mismatch	fn	core
E0214	missing-record-field	type	core
E0215	unknown-record-field	type	core
E0216	unknown-variant	type	core
E0217	int-literal-precision	type	core
E0218	for-over-non-list	type	core
E0219	bind-strict-prop	tile	forms
E0220	boundary-fallback-input	tile	lifecycle
E0225	radio-bind-without-value	tile	forms
E0226	input-bind-type	tile	forms
W0213	handler-on-inert-tile	tile	core
W0214	fmt-placeholder-argument-mismatch	all	stdlib
W0216	selection-beside-bind	tile	forms
E0301	missing-capability	effect	stdlib
E0302	unknown-capability	app	stdlib
E0303	invalid-cancel-target	effect	http
E0304	derived-slot	slot	core
E0305	fn-impurity	fn	core
E0306	err-type-not-text	effect	http
E0401	motion-unknown-property	tile	style
E0402	motion-invalid-timing	tile	style
E0403	motion-malformed	tile	style
E0601	duplicate-write	reducer	core
E0602	unassignable-member	reducer	core
E0701	a11y-button	tile	lifecycle
E0702	a11y-image	tile	lifecycle
E0703	a11y-link	tile	lifecycle
E0704	unknown-icon	tile	style
E0705	a11y-label-for	tile	lifecycle
E0712	episode-mock-invalid	effect	testing
E0713	test-shape-invalid	effect	testing
E0714	test-section-unknown	effect	testing
E0801	unimplemented-method	fn	stdlib
E0802	unimplemented-function	fn	stdlib
E0803	unimplemented-refinement	type	core
E0804	refinement-args-invalid	type	core

Feature examples — one runnable file per matrix cell

Layers name the definitions the example centers on; Spec links the section it demonstrates.

Example	Layers	Feature	Spec
01-slot-and-reducer.kumiki	slot, reducer	core	§1.4 §1.6
02-nominal-type.kumiki	type	core	§1.3
03-union-and-match.kumiki	type	core	§1.3
04-record-and-copy.kumiki	type	core	§1.3
05-pure-fn.kumiki	fn	core	§1.8
06-if-expression.kumiki	fn	core	§1.9
07-list.kumiki	fn	stdlib	§2.2.3
08-map.kumiki	fn	stdlib	§2.2.1
09-set.kumiki	fn	stdlib	§2.2.2
10-option.kumiki	fn	stdlib	§2.2.4
11-time-and-duration.kumiki	fn	stdlib	§2.2.8
12-layout.kumiki	tile	style	§4.4
13-text-input-bind.kumiki	slot, tile	forms	§5.1
14-select.kumiki	tile	forms	§5.5.1
15-checkbox.kumiki	tile	forms	§5.3.1
16-conditional-ui.kumiki	tile	core	§1.7
17-theme.kumiki	app	style	§4.2
18-routing.kumiki	app, tile	routing	§3.1
19-effect-http.kumiki	effect	http	§6.2
20-effect-storage.kumiki	effect	http	§6.7
21-timer.kumiki	reducer	lifecycle	§7.1.5
22-result.kumiki	type	stdlib	§2.2.5
23-lifecycle-route-enter.kumiki	reducer	routing	§3.4
24-fold.kumiki	fn	stdlib	§2.2.3
25-stop-timer.kumiki	effect, reducer	lifecycle	§7.1.5
26-overlay.kumiki	tile	stdlib	§2.3.7
27-custom-capability.kumiki	app, effect	stdlib	§2.5
28-tests.kumiki	reducer	testing	§8.1
30-motion.kumiki	tile	style	§4.9
31-argless-methods.kumiki	fn	stdlib	§2.2
32-panic-boundary.kumiki	tile, app	lifecycle	§7.3
33-field-vs-method.kumiki	fn, type	stdlib	§2.2
34-builtin-tiles.kumiki	tile	stdlib	§2.3
35-match-and-args.kumiki	tile, type	core	§1.9
36-effect-indexed-db.kumiki	effect	http	§6.7.4
37-lifecycle-events.kumiki	reducer	lifecycle	§7.1
38-confirm-leave-guard.kumiki	reducer	routing	§3.5.2
39-effect-session.kumiki	effect	http	§6.7.4
40-nested-routes.kumiki	app, tile	routing	§3.6
40-token-refs.kumiki	tile	style	§4.3
41-link-prefetch.kumiki	tile	routing	§3.8
42-scroll-restoration.kumiki	app	routing	§3.9
43-file-upload-preview.kumiki	tile	forms	§5.10
44-episode-test.kumiki	effect	testing	§8.6
45-ui-key-hover-tuple.kumiki	reducer, tile	core	§1.6
46-stdlib-paren-methods.kumiki	fn	stdlib	§2.2
47-icon-set.kumiki	tile	style	§4.8
48-effect-cancel.kumiki	effect	http	§6.4
49-ui-focus-blur.kumiki	reducer, tile	core	§1.6
50-match-pattern-integrity.kumiki	type	core	§1.9
51-selector-id.kumiki	reducer	core	§1.6.2
52-selector-id-arg.kumiki	reducer	core	§1.6.2
53-keyed-list-identity.kumiki	tile	core	§10.3.10
54-select-preserves-state.kumiki	tile	core	§10.3.11
55-video-preserves-currenttime.kumiki	tile	core	§10.3.11
56-details-preserves-open.kumiki	tile	core	§10.3.11
57-editable-preserves-focus.kumiki	tile	core	§10.3.11
58-unkeyed-conditional-rebuild.kumiki	tile	core	§10.3.12
59-overlay-keyed-layers.kumiki	tile	core	§10.3.10
60-empty-state-keyed-list.kumiki	tile	core	§10.3.10
61-reserved-identifier-names.kumiki	fn, reducer	core	§1.2
62-conditional-inline-tile-handlers.kumiki	tile, reducer	core	§10.3.13
63-reducer-batch-atomicity.kumiki	slot, reducer	core	§10.3.3
64-init-slot-argument.kumiki	app, effect	core	§1.12
65-prefers-dark.kumiki	app, reducer	style	§4.6.1
66-value-types.kumiki	type, slot, fn	core	§1.9.4
67-self-reference.kumiki	type, slot, tile, fn	core	§1.3.6
68-name-uniqueness.kumiki	type, slot, fn	core	§1.3.1
69-builtin-effect-capabilities.kumiki	reducer, effect	stdlib	§2.6
70-spec-grammar.kumiki	type, slot, fn, reducer	core	§1.2
71-button-type.kumiki	slot, reducer, tile	forms	§5.2.2
72-time-format.kumiki	slot, fn, tile	stdlib	§2.2.8
73-effect-policy-queue.kumiki	slot, effect, reducer	lifecycle	§10.4.3
74-common-tile-props.kumiki	slot, reducer, tile	style	§2.3.10
75-paren-less-stdlib-constants.kumiki	slot, effect, reducer	http	§6.1.4
76-conditional-adds-a-universal-handler.kumiki	slot, reducer, tile	core	§10.3.11
77-int-float-math.kumiki	slot, reducer, tile	stdlib	§2.2.7
78-editable-input-selector.kumiki	slot, reducer, tile	core	§W0212
79-option-get-assignment.kumiki	slot, reducer, tile	core	§1.6.3
80-route-in-tests.kumiki	slot, effect, reducer, tile	testing	§8.2.5
81-http-config-from-slots.kumiki	slot, effect, reducer, tile	http	§6.3.1
82-handler-on-a-user-tile.kumiki	slot, reducer, tile	core	§1.7.3
83-let-shadowing.kumiki	slot, reducer, fn, tile	core	§1.6.7
84-off-origin-link.kumiki	app, tile	routing	§3.3.1
85-capitalised-reducer-handler.kumiki	slot, reducer, tile	core	§1.7.3
86-container-selector-through-reference.kumiki	slot, reducer, tile	core	§1.6.2
87-replayed-environment-read.kumiki	slot, reducer, tile	core	§10.5.1
88-string-formatting.kumiki	slot, reducer, tile	stdlib	§2.4.5
89-qualified-show.kumiki	type, slot, reducer, tile	stdlib	§2.4.3
90-refinement-validation.kumiki	type, slot, reducer	forms	§5.6
91-conjoined-refinements.kumiki	type, slot, reducer, tile	core	§1.3.1
92-outlet-error-boundary.kumiki	slot, reducer, tile, app	lifecycle	§7.3
93-panic-info.kumiki	slot, reducer, tile, app	lifecycle	§7.2.3
94-editable-key-focus-blur-selectors.kumiki	slot, reducer, tile	core	§W0212
95-disabled-controls-refuse-a-step.kumiki	slot, reducer, tile	testing	§8.10
96-shortcut-named-fields.kumiki	type, slot, reducer, tile	core	§1.6.3
97-get-or-two-readings.kumiki	slot, reducer, tile	core	§2.2.1
98-receiver-decided-results.kumiki	slot, reducer, tile	core	§2.2
99-route-into-a-slot.kumiki	slot, fn, reducer, tile	routing	§E0304
100-option-filter.kumiki	slot, reducer, tile	stdlib	§2.2.4
101-list-index-write.kumiki	type, slot, reducer, tile	core	§1.6.3
102-non-text-keys.kumiki	type, slot, reducer, tile	stdlib	§2.2.2
103-generic-alias-refinement.kumiki	type, slot, reducer, tile	core	§1.3.1
104-nested-refinements.kumiki	type, slot, reducer, tile	core	§1.3.3
105-refused-bind.kumiki	slot, reducer, tile	forms	§5.1.2
107-builtin-content-is-positional.kumiki	slot, reducer, tile	core	§1.7.1
108-call-site-handler-joins-lifted.kumiki	slot, reducer, tile	core	§1.7.3
109-control-key-focus-blur-selectors.kumiki	slot, reducer, tile	core	§W0212
110-parse-by-base.kumiki	type, slot, reducer, tile	stdlib	§2.4.3
111-applied-type-qualifier.kumiki	type, slot, reducer, tile	stdlib	§E0124
113-match-value-type.kumiki	type, slot, reducer, fn, tile	core	§1.9
114-unit-value.kumiki	slot, reducer, fn, tile	stdlib	§2.1
115-fn-name-fragment.kumiki	slot, reducer, fn, tile	core	§1.8.6
116-emit-id-after-key-write.kumiki	slot, effect, reducer, tile	http	§6.4
119-effect-payload-bind-types.kumiki	type, slot, effect, reducer, tile	core	§1.6.5
120-http-config-value-types.kumiki	slot, effect, reducer, tile, app	http	§6.3.1
121-boundary-fallback-input.kumiki	type, slot, reducer, tile	lifecycle	§7.3
122-value-equality.kumiki	type, slot, reducer, tile	core	§1.9.4
123-one-key-per-value.kumiki	type, slot, reducer, tile	stdlib	§2.2.1
124-set-literal.kumiki	type, slot, reducer, tile, fn	stdlib	§2.2.2
127-http-query-string.kumiki	type, slot, effect, reducer, tile	http	§6.1.2
128-http-body-variants.kumiki	slot, effect, reducer, tile	http	§6.1.3
129-http-decode-failure.kumiki	type, slot, effect, reducer, tile	http	§6.5
130-storage-remove-clear.kumiki	slot, effect, reducer, tile	http	§6.7.2
132-toggle-bind.kumiki	type, slot, reducer, tile	forms	§5.1.1
133-typed-input-bind.kumiki	type, slot, reducer, tile	forms	§5.1.1
134-record-field-bind.kumiki	type, slot, tile	forms	§5.6
135-form-submit-gate.kumiki	slot, reducer, tile	forms	§5.2.2
136-submit-button-click.kumiki	slot, reducer, tile	forms	§5.2.2
139-get-unwrap-with-parentheses.kumiki	slot, reducer, tile	stdlib	§2.2.4
140-is-empty-both-spellings.kumiki	slot, reducer, tile	stdlib	§2.2.1
141-el-kebab-prop.kumiki	type, slot, reducer, tile	core	§1.6.5
142-tile-body-own-scope.kumiki	type, slot, reducer, tile	core	§1.7.2 inv. 1
143-fn-positional-arguments.kumiki	slot, reducer, fn, tile	core	§1.6.5
144-builtin-effect-input.kumiki	slot, reducer, tile	stdlib	§2.6
145-receiver-members.kumiki	slot, reducer, tile	stdlib	§2.2.3
153-route-specificity.kumiki	slot, reducer, tile, app	routing	§3.1.2
154-ssr-redirect.kumiki	tile, app	routing	§3.10
155-leave-on-param-change.kumiki	slot, reducer, tile, app	routing	§3.4
156-heading-level.kumiki	slot, reducer, tile	stdlib	§2.3.2
157-theme-switch.kumiki	slot, reducer, tile, app	style	§4.6
158-responsive-breakpoints.kumiki	tile, app	style	§4.5
159-replayed-event-payload.kumiki	type, slot, effect, reducer, tile	core	§10.5.3
160-tile-test-content-fields.kumiki	slot, tile	testing	§8.4
161-reducer-reads-its-own-write.kumiki	type, slot, reducer, tile	core	§1.6.4
162-fragment-binds-by-type.kumiki	slot, reducer, tile	stdlib	§2.2.3
163-keyed-list-tile.kumiki	type, slot, reducer, tile	core	§10.3.10
164-decode-refused-value.kumiki	type, slot, effect, reducer, tile	http	§6.7.2
165-sort-by-text-key.kumiki	type, slot, reducer, tile	stdlib	§2.2.3
166-map-map.kumiki	slot, reducer, tile	stdlib	§2.2.1
167-time-parse-calendar.kumiki	slot, reducer, fn, tile	stdlib	§2.2.8
168-map-index-absent-key.kumiki	type, slot, reducer, tile	core	§1.6.3
169-for-repeated-values.kumiki	slot, reducer, tile	core	§10.3.10