IF

The IF instruction executes a group of statements conditionally.

Syntax

IF condition THEN
   statement
   [...]
[ ELSE
   statement
   [...]
]
END IF

condition is a boolean expression.
statement is any instruction supported by the language.

Usage

If condition is TRUE, the runtime system executes the block of statements following the THEN keyword, until it reaches either the ELSE keyword or the END IF keywords and resumes execution after the END IF keywords.

If condition is FALSE, the runtime system executes the block of statements between the ELSE keyword and the END IF keywords. If ELSE is absent, it resumes execution after the END IF keywords.

By default, the runtime system evaluates all part of the condition. The semantics of boolean expressions can be controlled by the OPTIONS SHORT CIRCUIT compiler directive, to reduce expression evaluation when using AND / OR operators.

A NULL expression is considered as FALSE. Use the IS NULL keyword to test if an expression is null.

Example

MAIN
  DEFINE name CHAR(20)
  LET name = "John Smith"
  IF name MATCHES "John*" THEN
    DISPLAY "The name starts with [John]!"
  ELSE
    DISPLAY "The name is " || name || "."
  END IF
END MAIN