Appendix B: Keywords

Every reserved keyword in Archlang, split by where it’s recognized.

Keywords in .arch files

Keyword	Context	Effect	Chapter
type	Top-level	Declares a type	15
in	Module / process header	Attaches declaration to a parent module declared elsewhere	4, 7
labels	Body	Opens a labels block	9
required	Type body	Mandatory blank — instance must fill or drop	16
cascade	Type body, field modifier	Field value flows to descendants with override semantics	17
cascade *	Type body, field modifier	Declares a cascade-group root; sub-fields under the path are part of the group and replacement of the root drops the group	17
append	Type body, field modifier	Field value composes with descendants’ values	17
override	Body	Replace inherited entity with non-subtype kind	18
drop	Body	Remove inherited entity from this scope and below	18
subscribes	Interface body	Wire handler to an event interface	5
process	Top-level / module body	Declares a process	7
subprocess	Top-level / module body / process body	Declares a reusable subprocess	7
do	Process body	Invoke a subprocess	7
if, else	Process body	Conditional branch	7
switch	Process body	Multi-way branch by case label	7
parallel	Process body	Concurrent branches	7
each	Process body	Iterate over a collection	7
try, catch	Process body	Error path	7
fail, finish	Process body	Terminate process with explicit outcome	7
view	Top-level	Declares a view	8
focus	View body	Include only nodes matching the label	8
group	View body	Group by label (used with by)	8
by	View body	Companion to group	8
layout	View body	Pick layout algorithm	8
include	View body	Include nodes matching glob pattern	8
exclude	View body	Exclude nodes matching glob pattern	8
true, false	Field/label values	Boolean literals	9

Keywords in package.archspace files only

Keyword	Context	Effect	Chapter
use	Manifest / .arch file	Import types from another package	11
from	use clause	Names source package	11
as	use clause	Local rename	11
export	Type declaration / use clause	Make type visible to importers / re-export	11, 15
dependencies	Manifest	Opens dependencies block	11

name, version, and widgets are recognized as manifest field names but are not reserved — they don’t shadow identifiers anywhere.

Context-restricted keywords

Some keywords are only legal in specific bodies. Use outside that context is a parse error.

Keyword	Legal only in
if, else, switch, each, try, catch, parallel, do, fail, finish	Process bodies
focus, group, by, layout, include, exclude	View bodies
subscribes	Interface bodies
cascade, append, required	Type bodies

What’s not a keyword

User-defined kinds — service, database, command, query, etc. — are not keywords. They’re identifiers introduced by type module … / type facet … / type interface … declarations. The parser resolves them contextually against the active kind registry.

The three base kinds module, facet, interface are likewise not keywords. They appear as parent kinds in type module service { … } and can be used directly to declare generic instances.

Reserved keyword names

User-defined kinds, fields, and labels cannot reuse reserved keywords. Attempting to declare type module process { ... } or use required as a label name is a parse error.

See also

• Appendix A: Grammar — EBNF for every construct
• Appendix C: Stdlib kinds — built-in kinds (not keywords, but conventionally available)