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'THEN' expected

Velox reports 'THEN' expected when it has parsed the condition following if but the next token is not the then keyword. then separates the Boolean condition from the single statement or begin..end block controlled by that condition.

Example​

procedure ScriptEvent(var Value: Variant);
begin
  if Value = ''
    Value := 'default'; // Error: 'THEN' expected
end;

Add the keyword after the complete condition:

if Value = '' then
  Value := 'default';

How Velox detects it​

ProcessIf advances past if and asks the expression compiler to calculate up to token then. If an expression is produced but the current token is not then, it frees the temporary expression and emits ecThenExpected. Only this if compiler path emits the diagnostic.

After accepting then, the compiler writes the condition into its Boolean working register and emits the conditional branch. A condition that cannot be converted to the registered Boolean type can therefore report Type mismatch after the keyword issue is fixed.

Correction procedure​

  1. Check that the condition before the reported token is complete.
  2. Balance any parentheses and finish comparisons or function calls.
  3. Add then immediately before the controlled statement.
  4. For multiple controlled statements, enclose them in begin..end.
  5. In an if..then..else, do not put a semicolon immediately before else.

Edge cases and quirks​

  • A malformed condition can emit another expression diagnostic before the compiler reaches this check.
  • Newlines have no special terminating meaning; then is still required even when the controlled statement starts on the next line.
  • Nested if statements associate each else with the nearest unmatched if; use begin..end to make a different structure explicit.
  • Velox enables short-circuit Boolean evaluation, but that affects runtime operand evaluation, not the requirement for then.
  • if - conditional-statement syntax and execution.
  • if..else - branch association and semicolon rules.
  • Semicolon (';') expected - statement separation after the complete conditional.
  • Type mismatch - the parsed condition is not Boolean-compatible.

External references​