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0002-LexicalStructure.md

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0002-LexicalStructure.md

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Lexical Structure

Identifiers

Start with letter or underscore, followed by letters, digits, or underscores.

ID := [a-zA-Z_][a-zA-Z0-9_]*

Keywords

fn let mut type import match if then else case of extern

Literals

Integer Literals

INTEGER := [0-9]+

Examples:

let count = 42
let negative = -17
let zero = 0

Float Literals

FLOAT := [0-9]+ '.' [0-9]+ ([eE] [+-]? [0-9]+)?
       | [0-9]+ [eE] [+-]? [0-9]+

Examples:

let pi = 3.14159
let temperature = -273.15
let scientific = 6.022e23
let small = 1.5e-10

Type Inference:

  • Integer literals without decimal point infer to int
  • Literals with decimal point or scientific notation infer to float

String Literals

STRING := '"' (CHAR | ESCAPE_SEQUENCE)* '"'
ESCAPE_SEQUENCE := '\n' | '\t' | '\r' | '\\' | '\"'

Interpolated String Literals

INTERPOLATED_STRING := '"' (CHAR | INTERPOLATION)* '"'
INTERPOLATION := '${' EXPRESSION '}'

List Literals

LIST := '[' (expression (',' expression)*)? ']'

Examples:

let numbers = [1, 2, 3, 4]  // Fixed size: 4 elements
let names = ["Alice", "Bob", "Charlie"]  // Fixed size: 3 elements
let pair = [x, y]  // Fixed size: 2 elements

Operators

Arithmetic Operators

All arithmetic operators return Result types to handle overflow, underflow, and division by zero.

Integer Operations:

  • + Addition: (int, int) -> Result<int, MathError>
  • - Subtraction: (int, int) -> Result<int, MathError>
  • * Multiplication: (int, int) -> Result<int, MathError>
  • / Division: (int, int) -> Result<float, MathError> — always returns float
  • % Modulo: (int, int) -> Result<int, MathError>

Floating-Point Operations:

  • +, -, *, /, %: (float, float) -> Result<float, MathError>

Type Safety:

  • No automatic type promotion between int and float
  • Use toFloat(int) and toInt(float) for explicit conversion
  • Division / always returns float, even for integer operands

Examples:

let sum = 5 + 3           // Result<int, MathError>
let quotient = 10 / 3     // Result<float, MathError> - returns 3.333...
let remainder = 10 % 3    // Result<int, MathError> - returns 1

let precise = 10.0 / 3.0  // Result<float, MathError>
let divZero = 10 / 0      // Result<float, MathError> - Error(DivisionByZero)

Comparison Operators

  • == Equality
  • != Inequality
  • < Less than
  • > Greater than
  • <= Less than or equal
  • >= Greater than or equal

Logical Operators

  • && Logical AND (short-circuit evaluation)
  • || Logical OR (short-circuit evaluation)
  • ! Logical NOT

Assignment Operator

  • = Assignment

Other Operators

  • => Lambda/Match arm arrow
  • | Union type separator
  • :: Type annotation

Delimiters

  • ( ) Parentheses
  • { } Braces
  • [ ] Brackets
  • , Comma
  • : Colon
  • ; Semicolon
  • . Dot