Appendix A: Keywords

The following words are reserved by the Termina language and cannot be used as identifiers. They are listed here by the role they play.

Type names

Keyword	Role
u8 u16 u32 u64	Unsigned integer types
i8 i16 i32 i64	Signed integer types
usize	Unsigned machine-word integer
f32 f64	Floating-point types
bool	Boolean type
char	Character type
unit	The empty type (internal; not written in user code)

Type definitions

Keyword	Role
struct	Structure definition
enum	Enumeration definition
interface	Interface definition
class	Class definition, combined with task, handler, or resource

Type qualifiers

Keyword	Role
box	Owned block allocated from a pool
loc	Located (memory-mapped) field
const	Constant declaration
constexpr	Compile-time constant expression

Components and ports

Keyword	Role
task	Task class definition or task instance declaration
handler	Handler class definition or handler instance declaration
resource	Resource class definition or resource instance declaration
emitter	Event emitter instance declaration
channel	Message queue instance declaration
access	Access port to a resource
sink	Event sink port
in	Message input port
out	Message output port
triggers	Names the action a sink or input port activates
provides	Lists the interfaces a resource class implements
extends	Interface extension

Functions and class members

Keyword	Role
function	Free function definition
extern	Declaration of a function implemented in C
noreturn	Qualifier of an extern function whose calls never come back
procedure	Interface-visible operation of a resource class
method	Private helper of a class
viewer	Private helper of a class that only reads self
action	Event response of a task or handler class
self	The receiving instance in a member's body

Statements and expressions

Keyword	Role
var	Mutable binding
let	Immutable binding
if / else	Conditional execution
match / case	Branching on a variant
for / while	Bounded iteration and its optional runtime guard
return	End of a body, with or without a value
continue	Tail transfer to another action of the same task
reboot	Platform-level system reset
as	Explicit type conversion
is	Variant test
true / false	Boolean literals
import	Module import

Reserved words

The words null, termina, option, and config are reserved by the toolchain and cannot be used as identifiers, although they do not currently appear in user programs. The word termina also names the module namespace of the language: no module of a project may be placed under it, so src/termina/util.fin, imported as termina.util, is rejected.

Names taken by the generated C

The transpiler does not rename the identifiers of a program. A function called checksum in Termina is a function called checksum in the generated C, so the generated code can be read side by side with the source, and a debugger or a static analyzer reports the names the programmer wrote. Every Termina identifier therefore shares one name space with everything the generated code can see, and the transpiler rejects the names that are already taken there. These are the keywords of C, such as static or volatile, and the identifiers of the C standard library, such as memcpy or abs. The C standard also keeps for the compiler and its library any name that begins with an underscore followed by an uppercase letter, and the headers of the target platform declare names of their own.

The names of the platform headers depend on the platform selected in termina.yaml. The function index, for example, is declared by <strings.h>, which the POSIX and RTEMS platforms bring in through <string.h>, so a function named index is accepted when the project targets freertos10-stm32l432-nucleol432kc and rejected when it targets posix-gcc:

error [SE-218]: reserved identifier.
→ src/lib/util.fin:1:1
  │
1 │ function index(x : u32) -> u32 { return x; }
  │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The identifier index is declared by the headers of the target platform posix-gcc.

Each platform contributes a few hundred names, which change with the version of its toolchain, so the lists are not reproduced here. The error message states which group a rejected name belongs to and, for the platform group, which platform declares it.

Double underscores

Identifiers and module names cannot contain two consecutive underscores. The transpiler uses the double underscore as a separator in the names it builds: the variant Idle of an enum Mode becomes Mode__Idle in C, an Option<u32> becomes Option__u32, and every type and function that the generated code shares with the OSAL begins with termina__. Since no Termina identifier can contain the separator, none can coincide with a generated name. A single leading underscore is still allowed, as in the unused parameters of Appendix D, provided it is not followed by an uppercase letter.