Reserved Keywords

The lexer keyword map contains 41 entries. Most cannot be used as names. The four contextual testing words remain legal identifiers where a testing marker is not expected; their reservation is contextual, not global. case is an ordinary identifier, not a keyword. No words are released by this diagnostic change.

A reserved word in a parameter name produces PAR_RESERVED_KEYWORD at that word. The invalid parameter is dropped for parser recovery; the source still fails checking. Record-type fields retain PAR_FIELD_NAME_EXPECTED with a reservation explanation. Rename the parameter and all of its uses before checking again.

Complete keyword map

Word	Current use or reservation, owner and trigger
func	Function declaration or parenthesized function literal.
pure	Pure function marker.
let	Immutable binding.
letrec	Recursive binding.
in	Binding scope.
if	Conditional or match guard.
then	Conditional true branch.
else	Conditional false branch.
match	Pattern matching with braces (no with).
with	PAR019 dialect detection and planned effect-handler syntax. Handler lane: consume or release at syntax freeze. Alternatives: using, given, w.
type	Type declaration.
class	Type-class declaration syntax.
instance	Type-class instance syntax.
module	Module declaration.
import	Import declaration.
export	Export marker.
extern	External declaration.
forall	Universal type quantification.
exists	Reserved for existential type quantification; the type-system lane must consume or release it at syntax freeze.
test	Contextual named test marker; also a legal identifier.
tests	Contextual test block marker; also a legal identifier.
property	Contextual property marker; also a legal identifier.
properties	Contextual property block marker; also a legal identifier.
assert	Reserved for planned assertion builtin; assertion/testing lane must consume or release at syntax freeze. Alternatives: check, verify.
spawn	Reserved for planned concurrency lane (CSP/session types). Consume or release at concurrency syntax freeze. Alternatives: chan, fork, concurrent, pick.
parallel	Reserved for planned concurrency lane (CSP/session types). Consume or release at concurrency syntax freeze. Alternatives: chan, fork, concurrent, pick.
select	Reserved for planned concurrency lane (CSP/session types). Consume or release at concurrency syntax freeze. Alternatives: chan, fork, concurrent, pick.
channel	Reserved for planned concurrency lane (CSP/session types). Consume or release at concurrency syntax freeze. Alternatives: chan, fork, concurrent, pick.
send	Reserved for planned CSP/session-types lane. CSP lane: consume or release at syntax freeze. Alternatives: tx, rx, deadline, expires.
recv	Reserved for planned CSP/session-types lane. CSP lane: consume or release at syntax freeze. Alternatives: tx, rx, deadline, expires.
timeout	Reserved for planned CSP/session-types lane. CSP lane: consume or release at syntax freeze. Alternatives: tx, rx, deadline, expires.
as	Import alias.
deriving	Type-class derivation.
requires	Precondition contract.
ensures	Postcondition contract.
invariant	Invariant contract.
true	Boolean literal.
false	Boolean literal.
not	Boolean negation.
and	Boolean conjunction.
or	Boolean disjunction.

Reservation decisions

The effect-handler lane owns the proposed handle ... with syntax. Its syntax freeze must explicitly consume with as syntax or release it. This is separate from its current PAR019 role: match x with { ... } is rejected with the existing dialect diagnostic; AILANG uses match x { ... } and guards use if.

The CSP/session-types lane owns channel communication and concurrency reservations. Its examples are unfrozen sketches, including function-form receive/send; they do not establish that those words need keyword status. At syntax freeze the lane must explicitly consume or release each listed word. The assertion/testing lane has the same obligation for its planned assertion builtin (see the named-test assertion plan). No syntax-freeze decision is made here. Until its owner rules, each reservation remains. A release must update the keyword map, token enum, token strings, IsKeyword, and this reference together.

Working rename example

module examples/runnable/reserved_keyword_names

pure func combine(a: int, rx: int, b: int) -> int = a + rx + b
pure func usingValue(using: int) -> int = using
export pure func main() -> int = combine(1, 2, 3) + usingValue(4)

Use ailang check examples/runnable/reserved_keyword_names.ail to check the corrected three-parameter call. Recovery of an invalid parameter is not a successful type check and does not preserve a three-argument call's arity.

See Language Syntax, or run ailang prompt for the current teaching prompt and ailang check file.ail for diagnostics.