32.2.5. Procedural Functions

The following are functions that provide procedural programming capabilities as found in languages such as FORTRAN and C.

Important: In the descriptions below, items enclosed in square brackets [ ] are optional. If you choose to include the optional information, do not include the square brackets, only the items within them.

If...then...else function
CLIPS provides an if...then...else structure to allow for conditional execution of a set of actions.
The syntax is
```
 (if <expression>
   then
      <action>
   [else
      <action>]
 ) 
```
Any number of allowable actions can be used inside of the then and else portions, including other if...then...else structures. The else portion is optional. If <expression> evaluates to anything other than the symbol FALSE, then the actions immediately following the then are executed.
Otherwise, the actions following the else are executed. Although the if function returns a value, it is not useful in Ansys Polyflow.
Example:
This function sets the local variable ?Val to 3. if the variable ?v is equal to 6, and sets ?Val to 1. otherwise. In addition to =, you can use the comparison operators <, >, <=, and >=.
```
(if (= ?v 6)
  then
    (bind ?Val 3.)
 else
    (bind ?Val 1.)
) 
```
While
The while function is provided to allow simple looping. Its use is similar to that of the if function.
The syntax is
```
(while <expression>[do]
  <action>) 
```
Any number of functions can be included in the <action>. The symbol do can appear after the <expression> but it has no effect on the function.
If <expression> is evaluated to FALSE, then the function stops and does nothing. If <expression> is not FALSE, then <action> is executed. Then <expression> is reevaluated: if FALSE, the function stops; if not FALSE, <action> is executed again, and the process continues until <expression> evaluates to FALSE.
Example:
```
(while (< ?v 10)
   (bind ?v (- (* ?v ?v) 10))
) 
```
This function take the value of v and, if it less than 10, repeatedly replaces it with the value of -10 until v is greater than 10.
Loop-for-count
The loop-for-count function is provided to allow simple iterative looping.
The syntax for this function is
```
 (loop-for-count <range-spec>[do]<action>) 
```
where <range-spec> has the syntax
```
<end-index> | (<loop-variable>[<start-index><end-index>]) 
```
where <start-index> and <end-index> are integer expressions.
Any number of functions and expressions can be included in the <action>.
Example 1:
```
 (loop-for-count 5 (bind ?X1 (sin ?X1))) 
```
This example replaces ?X1 by the value of .
Example 2:
```
(deffunction PowerSeries4 (?x)
  (bind ?y 0)
  (loop-for-count (?Count 0 4) do
    (bind ?y (+ ?y (** ?x ?Count)))
  )
  ?y
)
```
This example takes a number and returns