Syntax:

          IF lexpr THEN
             statement_block
          [ ELSIF lexpr2 THEN
             statement_block ]
          [ ELSE
             statement_block ]
          END IF

This creates a test, or series of tests. The statement_block under the first lexpr that evaluates to 1 will be executed. Any number of ELSIF clauses are allowed. If no lexpr evaluates to true and the ELSE clause exists, the statement_block for the ELSE clause will be executed.

A special case of the IF statement is when any lexpr is a constant 0. In this case, the statement block is not parsed. This can be used for block comments.

          IF 0
             this is a dummy block that won't even be parsed!
          END IF

Example:

          IF x == 5 THEN
             y = 7
          ELSIF x == 6 THEN
             y = 12
          ELSE
             y = 0
          END IF