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repeat loop

Use repeat..until when a sequence must execute at least once and then repeat until a Boolean condition becomes True.

Syntax​

repeat
  Statement1;
  Statement2;
until BooleanExpression;

The region between repeat and until already accepts a statement sequence; an additional begin..end wrapper is not required.

How it works​

TPSPascalCompiler.ProcessRepeat marks the start of the body, compiles statements until the until token, then emits the condition calculation. A false result jumps back to the body; a true result continues after the loop.

break jumps after the loop. continue jumps to the condition calculation, not directly to the first body statement. The condition therefore still determines whether another iteration begins. Boolean and and or use Velox short-circuit evaluation.

Example​

procedure ScriptEvent(var Value: Variant);
var
  Attempts: Integer;
begin
  Attempts := 0;
  repeat
    Attempts := Attempts + 1;
  until Attempts >= 3;
  Value := Attempts;
end;

The body runs three times. Even if Attempts began at 3, it would be incremented once before the first test.

Common mistakes​

  • Writing a continuation condition as though this were while. The loop stops when the until condition is true.
  • Adding do after the condition; repeat..until has no do keyword.
  • Assuming continue skips the condition. It transfers control to that condition.
  • Forgetting that all statements up to until are in the body, regardless of indentation.

Edge cases and quirks​

  • The body always executes once before the first condition evaluation.
  • The semicolon before until is optional for the final body statement, but retaining it is clearer and consistent with generated examples.
  • A constant false condition creates an unbounded loop unless the body executes break or raises/exits. A constant true condition produces exactly one iteration.
  • Short-circuiting affects only Boolean and/or subexpressions. Evaluated Variant operands retain their normal conversion and Null/error behaviour.
  • The compiler patches structured break/continue jumps and rejects controls used outside a loop.

Errors and side effects​

A missing until, invalid condition or malformed body prevents compilation. Body side effects happen before every test, including the first. Runtime exceptions propagate unless an enclosing script try..except handles them.

Performance and concurrency​

Cost is at least one body execution plus one condition evaluation. No built-in timeout or iteration cap exists, so ensure some body path advances the termination condition. The loop is synchronous and adds no concurrency protection.

  • while loop — tests before the body and may run zero times.
  • for loop — counted iteration with automatic counter updates.
  • Boolean and Relational (Comparison) — build the termination condition.

External references​