Lexical Structure
This document describes the low-level lexical structure of Mux: tokens, keywords, identifiers, literals, and comments.
Source Files
Mux source files use UTF-8 encoding. File extension is .mux.
Case Sensitivity
Mux is case-sensitive. Keywords, identifiers, and type names must match the exact case as defined.
Whitespace
The only significant whitespace in Mux is the Newline character (\n), which separates statements. Other whitespace characters (space, tab, carriage return) are ignored except for separating tokens.
Multi-Line Comments
Multi-line comments start with /* and end with */. They can span multiple lines:
Multi-line comments do not nest. The first */ terminates the comment.
Identifiers
Identifiers name variables, functions, types, and other entities.
Rules
- Must start with a letter
- Can contain letters, digits, and underscores
- Cannot be a reserved keyword
Valid Identifiers
Note: Most Mux code uses snake_case, with some exceptions of course, but this is a convention, not a requirement.
Invalid Identifiers
Underscore Placeholder
The underscore _ is a special identifier used as a placeholder:
The underscore has special semantics:
- Cannot be read (assigning to
_discards the value) - Multiple uses of
_in the same scope do not conflict
Keywords
The following words are reserved keywords and cannot be used as identifiers:
Declaration Keywords
| Keyword | Purpose |
|---|---|
func | Function declaration |
returns | Return type specification for functions |
const | Constant declaration |
auto | Type inference declaration |
class | Class declaration |
interface | Interface declaration |
enum | Enum declaration |
common | Static/class method |
Control Flow Keywords
| Keyword | Purpose |
|---|---|
match | Pattern matching expression |
if | Conditional expression |
else | Else branch of conditional |
for | Iteration loop |
while | While loop |
break | Exit loop |
continue | Skip to next iteration |
return | Return from function |
Module Keywords
| Keyword | Purpose |
|---|---|
import | Module import |
as | Import alias |
Operator Keywords
| Keyword | Purpose |
|---|---|
is | Type constraint / interface implementation |
in | Membership test |
true | Boolean true literal |
false | Boolean false literal |
none | optional none literal |
some | optional some literal |
ok | result ok literal |
err | result error literal |
Special Keywords
| Keyword | Purpose |
|---|---|
self | Instance reference (inside class methods only) |
Literals
Integer Literals
Decimal integers:
Float Literals
Character Literals
Single Unicode code point in single quotes:
String Literals
UTF-8 sequences in double quotes:
Escape sequences:
\\- Backslash\"- Double quote\'- Single quote\n- Newline\t- Tab\r- Carriage return
Boolean Literals
none Literal
Operators and Punctuation
Arithmetic Operators
| Symbol | Meaning |
|---|---|
+ | Addition |
- | Subtraction / Negation |
* | Multiplication |
/ | Division |
% | Modulo |
** | Exponentiation |
Comparison Operators
| Symbol | Meaning |
|---|---|
== | Equality |
!= | Inequality |
< | Less than |
<= | Less than or equal |
> | Greater than |
>= | Greater than or equal |
Logical Operators
| Symbol | Meaning |
|---|---|
&& | Logical AND (short-circuit) |
| ` | |
! | Logical NOT |
Other Operators
| Symbol | Meaning |
|---|---|
= | Assignment |
+= | Compound assignment |
-= | Compound assignment |
*= | Compound assignment |
/= | Compound assignment |
%= | Compound assignment |
++ | Postfix increment |
-- | Postfix decrement |
. | Member access |
& | Reference creation |
* | Dereference |
Punctuation
| Symbol | Usage |
|---|---|
( ) | tuple literals, Grouping, function calls, parameters |
[ ] | List literals, indexing |
{ } | Block statements, map literals, set literals |
< > | Type parameters (generics) |
, | Separator |
Line Continuation
Mux does not support implicit line continuation. Each statement must be on its own line. The only way to continue an expression across lines is with explicit grouping:
See Also
- Language Guide - Practical examples