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while loop

Use while to repeat one statement while a Boolean condition remains True. The condition is tested before the first iteration, so the body may not run.

Syntax​

while BooleanExpression do
  Statement;

For a multi-statement body:

while BooleanExpression do
begin
  Statement1;
  Statement2;
end;

How it works​

TPSPascalCompiler.ProcessWhile emits the condition calculation at the start of the loop, converts/writes its result into the default Boolean temporary and conditionally jumps past the body when false. After the body, execution jumps back to the condition calculation.

break is patched to the instruction after the loop. continue is patched to the condition calculation, so it immediately performs the next test. Boolean and and or within the condition use Velox's short-circuit compiler option.

Example​

procedure ScriptEvent(var Value: Variant);
var
  Remaining: Integer;
begin
  Remaining := 3;
  while Remaining > 0 do
  begin
    Remaining := Remaining - 1;
  end;
  Value := Remaining;
end;

The body runs three times and leaves Value as 0.

Common mistakes​

  • Failing to change state used by the condition, creating an unbounded loop.
  • Expecting the body to run once when the condition starts false; use repeat..until for a post-test loop.
  • Using a non-Boolean Variant directly as the condition. Prefer an explicit comparison or registered value test.
  • Placing required progress logic after a continue; that logic is skipped.

Edge cases and quirks​

  • The condition is recalculated on every iteration and after every continue.
  • A false initial condition performs no body statements or their side effects.
  • Short-circuit Boolean guards can prevent evaluation of an unsafe right operand, but Variant conversion and evaluated function calls can still raise runtime errors.
  • The compiler detects break or continue outside a loop as an error. It also tracks invalid jumps across structured regions and can reject control flow that would enter or leave a loop unsafely.
  • Velox does not impose an iteration limit. Termination is entirely the script author's responsibility.

Errors and side effects​

Missing do, an incompatible condition or malformed body causes compilation to fail. Runtime exceptions in the condition or body leave the loop through normal script exception propagation. Calls made by the condition occur once per test unless short-circuited.

Performance and concurrency​

Total cost is the condition plus body cost multiplied by the number of tests/iterations. Cache invariant expensive data outside the loop. A tight loop can delay the map event that owns it, and the statement provides no cancellation polling or synchronisation by itself.

  • for loop — counted iteration.
  • repeat loop — post-test iteration that always executes once.
  • Boolean and Relational (Comparison) — condition construction and short-circuit rules.

External references​