OS/2 Procedures Language 2/REXX


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IF




 >>--IF-expression-+-+THEN-+-+instruction-+--------------------+---><
                   +;+     +;+            +-ELSE-+-+instruction+
                                                 +;+

IF is used to conditionally process an instruction or group of 
instructions depending on the evaluation of the expression. The expression 
must evaluate to 0 or 1. 
The instruction after the THEN is processed only if the result of the 
evaluation is 1. If you specify an ELSE clause, the instruction after ELSE 
is processed only if the result of the evaluation is 0. 
Example: 

if answer='YES' then say 'OK!'
                else say 'Why not?'

Remember that if the ELSE clause is on the same line as the last clause of 
the THEN part, you need a semicolon to terminate that clause. 
Example: 

if answer='YES' then say 'OK!';  else say 'Why not?'

The ELSE binds to the nearest IF at the same level. The NOP instruction 
can be used to eliminate errors and possible confusion when IF constructs 
are nested, as in the following example. 
Example: 

If answer = 'YES' Then
   If name = 'FRED' Then
      say 'OK, Fred.'
   Else
      nop
Else
   say 'Why not?'

Notes: 
   1. The instruction can be any assignment, command, or keyword 
      instruction, including any of the more complex constructs such as 
      DO, SELECT, or the IF instruction itself. A null clause is not an 
      instruction; so putting an extra semicolon after the THEN or ELSE is 
      not equivalent to putting a dummy instruction (as it would be in C). 
      The NOP instruction is provided for this purpose. 
   2. The symbol THEN cannot be used within expression, because the 
      keyword THEN is treated differently, in that it need not start a 
      clause.  This allows the expression on the IF clause to be 
      terminated by the THEN, without a semicolon being required.  If this 
      were not so, users of other computer languages would experience 
      considerable difficulties. 
   

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