Conditional Statements

IF and UNLESS select a runtime block from a condition. IF executes its first block when the condition is true; UNLESS executes its first block when the condition is false.

IF (temperature < minimum)
{
  temperature := minimum;
}

UNLESS (ready)
{
  initialize();
}

Conditions

The parenthesized expression must have type BOOL or be implicitly convertible to BOOL. Quxlang evaluates the expression once before selecting a branch. An explicit booliation expression such as pointer?? or pointer!? tests the affirmative or empty state of a pointer or another booliable type.

IF (buffer??)
{
  consume(buffer->);
}

UNLESS(condition) inverts branch selection; it does not change how the condition expression itself is evaluated.

ELSE chains

ELSE supplies the alternative block. It may be followed by another IF or UNLESS, producing one source-level chain:

IF (value < 0)
{
  category := -1;
}
ELSE IF (value == 0)
{
  category := 0;
}
ELSE UNLESS (value < maximum)
{
  category := 2;
}
ELSE
{
  category := 1;
}

Conditions are evaluated from left to right until one block is selected. Later conditions and all unselected blocks do not execute.

An IF chain uses ELSE, not STATIC_ELSE. Compile-time branches use the separate STATIC_IF and STATIC_ELSE syntax documented under Compile-Time Evaluation.

Branch scope and values

Each branch is a function block. Variables declared in that block are local to the block, and their lifetimes end when control leaves it. A name needed after the chain must be declared before the IF and assigned by the selected branch:

VAR magnitude I32;
IF (value < 0)
{
  magnitude := 0 - value;
}
ELSE
{
  magnitude := value;
}
use(magnitude);

The compiler converges the object state from all branches at the statement following the chain. Each reachable path must therefore leave later-used objects in a compatible lifetime state.

Relationship to other selection forms

• STATIC_IF selects during compile-time generation and discards the unselected source path.
• MATCH dispatches on a UNION or VARIANT alternative.
• INCLUDE_IF conditionally includes a declaration in the active source configuration.

Those forms have different evaluation times and cannot be substituted merely by changing the keyword on an IF statement.

Branch likelihood

Place LIKELY or UNLIKELY after IF or UNLESS and before the condition:

IF LIKELY (ready)
{
  process();
}
ELSE IF UNLIKELY (retry)
{
  retry_operation();
}

The hint describes the likelihood of entering that statement's first block. For UNLESS, that is the block entered when its condition is false. Hints inform optimization and do not change evaluation or branch semantics.