IfElse

Description:	Returns the result of one of two expressions depending upon the result of a conditional expression.
Returns:	Varies
Usage:	Script or steady state.
Function Groups:	Logic Control
Related to:	Ternary Operator (IfElse) \| Cond \| Execute \| IfThen
Format:	IfElse(Condition, TRUECase, FALSECase) or Condition ? TRUECase : FALSECase
Parameters:

Condition

Required. An expression that returns true or false. If true the TRUECase is executed. If false, the FALSECase is executed. If invalid, neither case is executed.

TRUECase

Required. The expression (typically an Execute statement) which is executed when Condition is true.

FALSECase

Required. The expression (typically an Execute statement) which is executed when the Condition is false.

Comments:

This is simply a different name for the Cond function. The return value is the result of the evaluated case. Both cases are evaluated, in which case Cond is a more apt name.

Writing long "If Else - Else - Else ... " expressions is not efficient and can be avoided in many situations.

A common task is to build a string based on the current value of one or more other tags. For this example, suppose that you need to build a message that varies by some situational ID and a matching state. The message will be a combination of a prefix that indicates the situation and a suffix that indicates the state. Monitoring the situation, you have tags [Situation ID] and [Current State]. A long and inefficient method might be to write:

[Situation ID] == 1 ? Concat("Prefix A ", 
                             [Current State] == 1 ? "[Suffix A]" :
                             [Current State] == 2 ? "[Suffix B]" :
                             [Current State] == 3 ? "[Suffix C]" ) 
                    :
[Situation ID] == 2 ? Concat("Prefix B ", 
                             [Current State] == 1 ? "[Suffix A]" :
                             [Current State] == 2 ? "[Suffix B]" :
                             [Current State] == 3 ? "[Suffix C]" ) 
                    :
 etc.

Instead of this, do the following:

1. Create a set of application properties for each situational prefix and state suffix:

 Situation1                       = Prefix A: 
 Situation2                       = Prefix B: 
 Situation3                       = Prefix C: 
 State1                           = [Suffix A]
 State2                           = [Suffix B]   (etc.)

2. Write an expression that concatenates the appropriate properties into a message based on the value of your two tags:

Concat(
  Variable(Concat("Situation", [Situation ID])),
  Variable(Concat("State", [Current State]))
)

No comparisons or If-Else statements are required. Those four lines of code can create as many combinations of situation prefixes and state suffixes as you need.

Scripting example:

If 1 Main;
[
  IfElse(i > 0 && i <= 50, 
         Execute(y[i] = x, 
         i++), 
  { else } 
         Execute(x = i,
                 doneFlag = 1) 
  ); 
]

This statement will set the element of array y equal to i and then increment i if i is between 1 and 50 inclusive. If i is not in that range, x will be set to i and doneFlag will go true. Note that Execute may only appear in a script.