IF...THEN...ELSE
================

Function
--------

**IF...THEN...ELSE...** executes either of two statements as the result
of an expression.

Syntax
~~~~~~

IF (expression) THEN (statement1) [ELSE (statement2)]

Examples
--------

::

   IF A=B THEN X=10 ELSE A=A+1
   IF D AND NOT B THEN C=0:GOTO 50 ELSE RETURN

Multiple statements separated with colons are implemented or skipped
depending on the condition.

::

   IF A=6 THEN IF B>10 THEN A=0 ELSE ELSE A=A+1

Omitting the first ELSE will move processing straight onto the next line
if the first condition is false (i.e. A=6) and cause A to be incremented
if A=6 and B>10.

Remarks
~~~~~~~

The expression must be able to be evaluated true or false. If the
expression is true then statement 1 is executed, and if false statement
2 is executed.

The statement may include other conditional statements (nested), but
care must be exercised in the positioning of ELSE to associate them with
the correct IF. Generally, each ELSE is associated with the most recent
IF. Extra ELSE statements causing no action at the end of the line may
be omitted.

The use of logical operators outlined in the section relating to
:doc:`if` are also allowed when using IF...THEN...ELSE.