A simple form for the IF construct is:
statement_block 2 ]
The ELSE section is optional. If the logical expression is true, the first block
is executed, otherwise the second.
Logical expressions are formed using relational
operators and logical operators knowing
their order of precedence.
Logical expressions can be stored as mLOGICAL
If the ELSE section consists of one IF construct, then ELSE and IF can be
reduced to ELSEIF provided that one of the associated ENDIFs is deleted.
Sometimes it is simpler to use a CASE construct.
IF constructs can be named. Optionally, the
same name may be used after ELSE and after ELSEIF (expr)