Keywords

Reserved

These words can never be a name. They can’t be used for a variable, a function, a parameter, a class, a field, a method, an import alias, a loop label or a sample in a pattern.

Keyword	What it is
let	Declares a variable. See Variables & Scope
fn	Defines a function. See Functions
return	Leaves a function with a value. See Functions
class	Defines a class. See Classes
use	Imports a module. See Modules
as	Renames an import. See Modules
private	Keeps a definition out of a module’s exports. See Modules
dsp	Starts a dsp definition. See DSP Blocks
if	Runs code when a condition holds. See Control Flow
else	The other branch of an if. See Control Flow
match	Picks a branch by value. See Control Flow
loop	Repeats until break. See Control Flow
do	Repeats a set number of times. See Control Flow
for	Iterates. See Control Flow
in	Names what for iterates. See Control Flow
break	Leaves a loop. See Control Flow
continue	Starts a loop’s next iteration. See Control Flow
assert	Stops with an error when a condition fails. See Control Flow
true	The Boolean true. See Values & Types
false	The Boolean false. See Values & Types
NUL	The absence of a value. See Values & Types
PLAY	Starts the play head. See Transport
PAUSE	Holds the play head where it is. See Transport
STOP	Returns the play head to the start. See Transport
RESET	Discards the whole session. See Transport
RECORD	Plays, and records the armed tracks. See Transport
SEEK	Moves the play head to a cycle. See Transport

Using a keyword as a name is a parse error, reported at the word:

let if = 7;
// → Parse error at 1:5: `if` is a keyword and cannot be used as a name

A keyword only counts when it stands as a whole word, so letter, iffy and PLAYING are all ordinary names.

DSP words

The words a dsp definition is made of, such as effect, param, state, input, output, range and process, are only keywords where that definition expects them. Everywhere else they are ordinary names. That includes the code inside a dsp definition, and functions such as track.set_input(...) and range(...).

let state = 1;
let input = range(0, 3);
assert state == 1;