Begin/End Block Statements

The begin/end statement is a block statement that does not perform any logic or functionality in itself, but is used to group two or more statements together so that they can be treated as a single statement – usually in a context where a single statement is expected.

For example, the if/then statement expects a single sub-statement after the then keyword, which will be executed if the condition preceding it evaluates to true. Using a begin/end pair, a whole block of statements can be tied to the condition instead. Technically speaking, the begin/end is not part of the if/then statement's syntax:

if x ≥ 0 then 
  DoSomething;             // if expects only a single sub-statement...

if x ≥ 0 then begin        // ...but a begin/end statement can be used for that single
  DoSomething;             // statement, allowing to conditionally execute a whole list
  DoSomethingElse;
end;

The following lists all statement and expression types that can be used in combination with an (optional) begin/end block:

• if/then/else statements, as well as their else clause
• for/do loops
• while/do loops
• Infinite loops with the loop keyword
• Individual clauses in a case statement
• locking statements
• using statements
• with/do statements
• async expressions
• Lambda expressions

By contrast, the following block statements already enclose a list of statements they act upon and do not require an explicit begin/end pair to act upon multiple statements at once:

• repeat/until block loops
• try/except/finally Exception Handling blocks

Statements vs. Expressions

Like all statements, begin/end blocks can only be used in a context where a plain statement is expected. They can not act as expressions, because they only represent a bunch of statements to be executed, but not a resulting value. Conversely, begin/end blocks can not be used in the following constructs:

• exit or yield statements
• As condition for if/then, while/do and repeat/until loops
• As loop expressions in for loops
• As expression for with, locking or using statements

Async Expressions and begin/end

async expressions are special in that they are expressions, but can take either an expression or a plain statement to be run asynchronously. When applied to a statement (as would be the case when using begin/end), the async keyword results in an expression of a type-less Future, also referred to as a Void Future.

You can read more about async expressions here.

Standalone begin/end Block Statements

Since begin/end blocks introduce no behavior or logic of their own, they can of course be also used to group one or more (technically, zero or more) statements at any place in code where a statement is allowed, even when not used in the context where the grouping is necessary to pull the statements together.

The following code snippet shows three statements, the second of which is a begin/end block that itself contains two statements. This is valid, even though the begin/end pair has no effect, and the code would perform the exact same action without it.

Console.Write('hello');
begin
  Console.Write(' to');
  Console.Write(' the');
end;
Console.WriteLine(' world')