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if..else

Use if..else when exactly one of two statement branches must run, selected by a Boolean condition.

Syntax​

if BooleanExpression then
  TrueStatement
else
  FalseStatement;

Use compound statements for multi-statement branches:

if BooleanExpression then
begin
  TrueStatement1;
  TrueStatement2;
end
else
begin
  FalseStatement1;
  FalseStatement2;
end;

There is deliberately no semicolon between the end of the true branch and else.

How it works​

The modified PascalScript compiler evaluates the condition into a Boolean temporary. A false result jumps to the else branch; a true result executes the first branch and then jumps past the alternative. Only one branch executes.

When if statements are nested without explicit blocks, an else binds to the nearest preceding if that does not already have an else. This is implemented by the compiler's one-line if sub-block and its handling of the else token. Use begin..end to make a different association explicit.

Boolean and and or within the condition use the Velox short-circuit setting, with the same operand and failure rules as a plain if.

Example​

procedure ScriptEvent(var Value: Variant);
var
  Score: Integer;
begin
  Score := 72;
  if Score >= 50 then
    Value := 'pass'
  else
    Value := 'review';
end;

Only one assignment is made. The example omits a semicolon after the true-branch assignment because the next token is else.

Common mistakes​

  • Writing a semicolon before else, including end; else. This closes the true statement and leaves an unmatched else; use end else.
  • Relying on indentation to pair an else with an outer if. The parser uses the nearest unmatched if, not visual alignment.
  • Repeating the same expensive or state-changing test in each branch. Evaluate it once into a local value when consistent results matter.
  • Using deeply nested branches where a case statement or an early guard would make the choices clearer.

Edge cases and quirks​

  • Either branch may be an empty statement, but an explicit empty compound block is clearer.
  • A branch may contain another if..else; use blocks whenever the intended pairing is not immediately obvious.
  • The condition is evaluated once, but only the chosen branch's calls and side effects occur.
  • Velox supports the statement form documented here. Do not assume newer Delphi conditional-expression syntax is accepted by the PascalScript parser.

Errors and side effects​

Compile-time errors include a missing then, unmatched else, invalid condition or incompatible assignment in either branch. Both branches must compile even though only one runs. Runtime exceptions propagate only from the evaluated condition and selected branch.

Performance and concurrency​

Branch overhead is negligible. Avoid hiding expensive dataset navigation or external module operations inside a condition whose cost is not obvious. if..else provides no synchronisation for shared objects.

  • if — executes a branch without an alternative.
  • case — expresses several mutually exclusive choices.
  • begin..end — groups multiple statements and disambiguates nested branches.
  • Boolean and Relational (Comparison) — form source-safe conditions.

External references​