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Walrus features a clean, expressive syntax that’s easy to read and write. This guide covers the basic syntax rules and commenting conventions.

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Comments

Walrus supports both single-line and multi-line comments to help you document your code.

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Single-line comments

Use // for single-line comments: 
// This is a single-line comment
let x = 42; // Comments can appear after code

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Multi-line comments

Use /* */ for multi-line comments that can span multiple lines: 
/* This is a multi-line comment
   that can span multiple lines */

let name = "Walrus";

/* Multi-line comments can also be inline */ let y = 84;
Multi-line comments are useful for longer explanations or temporarily disabling blocks of code during development.

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Statements and expressions

Walrus distinguishes between statements and expressions:
  • Statements perform actions (like variable declarations, assignments, function definitions)
  • Expressions evaluate to values (like arithmetic operations, function calls, literals)

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Statements

let x = 10;           // Variable declaration
x = x + 5;            // Assignment
println("Hello");     // Function call statement

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Expressions

2 + 3 * 4             // Arithmetic expression
len([1, 2, 3])        // Function call expression
x > 5 and y < 10      // Boolean expression

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Semicolons

Walrus does not require semicolons at the end of statements. Each statement is typically on its own line: 
let name = "Alice"
let age = 30
println(f"Hello, {name}!")

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Whitespace and indentation

While Walrus doesn’t enforce strict indentation rules like Python, proper indentation improves code readability, especially in control structures: 
if score >= 90 {
    println("Excellent!");
} else if score >= 70 {
    println("Good job!");
} else {
    println("Keep practicing!");
}

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Code blocks

Code blocks are delimited by curly braces { and }: 
if condition {
    // Code block for if
    let temp = x * 2;
    println(temp);
}

fn calculate : a, b {
    // Function body is a code block
    let result = a + b;
    return result;
}

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Identifiers

Identifiers (variable names, function names, etc.) must follow these rules:
  • Start with a letter (a-z, A-Z) or underscore (_)
  • Can contain letters, digits (0-9), and underscores
  • Case-sensitive (myVar and myvar are different)

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Valid identifiers

let count = 0;
let user_name = "Alice";
let _private = 42;
let value123 = true;

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Invalid identifiers

let 123value = 10;    // Cannot start with a digit
let my-var = 5;       // Hyphens not allowed
let my var = 5;       // Spaces not allowed

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Reserved keywords

The following words are reserved and cannot be used as identifiers:

Control flow

  • if
  • else
  • while
  • for
  • in
  • break
  • continue

Declarations

  • fn
  • let
  • struct
  • return
  • import
  • as

Literals & operators

  • true
  • false
  • void
  • and
  • or
  • not
Walrus provides two built-in functions for output:

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println

Prints a value followed by a newline: 
println("Hello, World!");
println(42);
println([1, 2, 3]);

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print

Prints a value without a newline: 
print("Count: ");
for i in 0..5 {
    print(str(i) + " ");
}
println("");  // Add newline at the end
Both print and println automatically convert values to strings for display.

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Best practices

Choose descriptive names that explain the purpose of the variable:
// Good
let user_count = 10;
let total_price = 99.99;

// Avoid
let x = 10;
let tmp = 99.99;
Add comments to explain why you’re doing something, not what you’re doing:
// Calculate discount based on loyalty tier
// Gold members get 20%, Silver get 10%
let discount = 0;
if tier == "gold" {
    discount = 0.20;
} else if tier == "silver" {
    discount = 0.10;
}
Break long expressions into multiple lines for better readability:
// Good
let total = base_price + 
            shipping_cost + 
            tax_amount;

// Less readable
let total = base_price + shipping_cost + tax_amount + insurance_fee + handling_charge;

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Next steps

Data types

Explore Walrus data types including integers, floats, strings, and collections

Variables

Learn how to declare and work with variables

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