AL Syntax Basic

Master AL syntax including comments, compound statements, code regions, and XML documentation comments.

30 minBeginner

Learning Objectives

Write single-line and block comments in AL
Use XML documentation comments for IntelliSense
Structure code with
Understand compound statements with begin/end

Comments in AL

Comments help other developers understand your code. AL supports two comment styles.

Single-line comments

Use double slashes // for single-line comments:

// This is a comment
CustomerNo := 'C00001'; // Inline comment

In VS Code, press Ctrl+/ to toggle line comments.

Block comments

Use /* and */ for multi-line block comments:

/*
    This is a block comment
    spanning multiple lines.
    Useful for longer explanations.
*/

Press Alt+Shift+A in VS Code to toggle block comments.

XML Documentation Comments

XML comments improve readability and enable IntelliSense in VS Code for anyone extending your code:

Email.Codeunit.al

/// <summary>
/// Provides functionality to create and send e-mails.
/// </summary>
codeunit 8901 "Email"
{
    /// <summary>
    /// Enqueues an email in the outbox to be sent in the background.
    /// </summary>
    /// <param name="EmailMessageId">The ID of the email to enqueue</param>
    procedure Enqueue(EmailMessageId: Guid)
    begin
        EmailImpl.Enqueue(EmailMessageId);
    end;
}

Documentation Best Practices

Never state the obvious — explain why, not what
Use active words: "Sets...", "Gets...", "Specifies..."
List preconditions for parameters
Document exceptions and side effects

Code Regions

Use #region and #endregion to organize large files:

#region Sales Processing
    local procedure ProcessSalesOrder(SalesHeader: Record "Sales Header")
    begin
        // Processing logic
    end;
#endregion

#region Purchase Processing
    local procedure ProcessPurchaseOrder(PurchaseHeader: Record "Purchase Header")
    begin
        // Processing logic
    end;
#endregion

Regions can be collapsed in VS Code for easier navigation — especially useful in large codeunits.

Compound Statements

A compound statement groups multiple statements between begin and end:

if Amount > 1000 then begin
    ApplyDiscount(Amount);
    LogTransaction(Amount);
    NotifyManager(Amount);
end;

Every if, repeat, while, and case that executes more than one statement requires begin/end.

Assignment and Expressions

AL uses := for assignment:

Total := Quantity * UnitPrice;
CustomerName := 'Contoso Ltd.';
IsValid := (Amount > 0) and (Amount < 10000);

Semicolons Required

Every statement in AL must end with a semicolon (;). Missing semicolons are one of the most common compile errors for beginners.

Naming Conventions

Follow Microsoft's AL coding guidelines:

Element	Convention	Example
Objects	PascalCase with quotes	`table 50100 "Customer Bonus"`
Procedures	PascalCase	`procedure CalculateTotal()`
Variables	PascalCase	`TotalAmount: Decimal`
Constants	PascalCase	`MaxRetryCount: Integer`

Next Steps

With syntax fundamentals covered, you'll set up your complete development environment in Module 2.

Learning Objectives

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