Create and Call Functions

Introduction

Functions are methods you build yourself and are comparable to JavaScript functions. They are a set of statements that perform a task or calculate a value and are useful to combine some functionality that you use multiple times in your ruleset. For example, let's assume that the travel insurance calculator needs to add extra costs depending on age that applies to both insurance and extra costs:

Age category	Extra costs per day
18 - 30	0.15
31 - 50	0.10
51 and older	0.05

You can wrap this up in an expression like this:

let extraCosts = 0;
if (Age >= 18 && Age < 31) {
  extraCosts = ROUND(NumberOfDays * ExtraCostPerDay18_30);
}
if (Age >= 31 && Age < 51) {
  extraCosts = ROUND(NumberOfDays * ExtraCostPerDay31_50);
}
if (Age >= 51) {
  extraCosts = ROUND(NumberOfDays * ExtraCostPerDay51AndUp);
}

And add this to both rules in Travel insurance calculator so that they use the extraCosts variable in their calculation.

But this has a major downside: if something changes to the age categories, you have to modify every rule where this code is used. In that case, it's better to create a function that calculates the extra costs, which you can (re)use from anywhere in your ruleset. If then something changes to the age categories, you only have to modify the function.

By the end of this tutorial, you'll know how to:

• Create a function.
• Call a function from a rule.

Create and call functions

Task: Add extra input and constants

Start with creating the following input and constants in your Travel insurance calculator ruleset:

Input

Name	Type
DateOfBirth	date

Constants

Name	Constant type	Value
ExtraCostPerDay18_30	Simple	0.15
ExtraCostPerDay31_50	Simple	0.10
ExtraCostPerDay51AndUp	Simple	0.05

Task: Create a function to calculate extra costs

Like methods, functions need input to operate on, and an input for a function is called a parameter. So when calling a function, you supply its parameters, and the function returns a calculated or determined result.

1. Create a function named AgeSurcharge, and in the Return type list, select number.

2. Click Add parameter.
   ↳ Rulecube adds a parameter row:

   

3. In the Name field, enter age, and in the Type list, select number.

4. Add a second parameter named numberOfDays, and set its Type to number.

5. In the Function body, copy and paste the following function:

   if (age >= 18 && age < 31) {
     return numberOfDays * ExtraCostPerDay18_30;
   }
   if (age >= 31 && age < 51) {
     return numberOfDays * ExtraCostPerDay31_50;
   }
   if (age >= 51) {
     return numberOfDays * ExtraCostPerDay51AndUp;
   }
   return 0;

   Explanation: Lines 1, 4 and 7 check the age parameter and lines 2, 5 and 8 calculate and return the result using the correct constant.
   IMPORTANT: Do not worry about the code if you do not fully understand it right now, in the next lesson we will replace this with a better and easier to understand solution!

6. Click Save.
   ↳ The function is ready for calling now.

If you prefer keyboard shortcuts, press Ctrl+S for saving.

Task: Add an Age rule

To prevent us from repeating ourselves, let's first create a rule that pre-calculates the current age based on the DateOfBirth input.

1. Add a new rule named Age with the following expression:

   AGE(DateOfBirth)

2. Disable the "Output" checkbox

Task: Call the AgeSurcharge function within your ruleset

1. Open the InsuranceCosts rule.

2. Change the expression to this code:

   ROUND(
     RiskCostsPerDay.get(RiskCategory) * NumberOfDays +
       AgeSurcharge(Age, NumberOfDays),
   );

3. Now change the expression for the ElectronicDeviceCosts rule to this code:

   ROUND(
     NumberOfDays * NumberOfItems * CostsPerItemPerDay +
       AgeSurcharge(Age, NumberOfDays),
   );

4. Save your ruleset and try it out in the sandbox.

You can save the input values you enter on the Sandbox page to reuse them in later try out sessions, which saves you time:

1. Enter the input values.
2. Click Save as.
   ↳ The Save input pop-up opens.
3. In the Name field, enter name for the input set.
4. Click OK.

In a later try-out session, in the Input list, select the name of the stored input set, and the stored values are filled into the corresponding input fields.

Recap

You've created functions that further sophisticate your rulesets and accelerate your development cycle.

What's next?

In the previous tutorials we've been developing our ruleset and trying it out in the Sandbox to test it. We want to make sure that it will continue to work as intended. We'd like to be notified when a change to our ruleset unknowingly changes its output.

Rulecube has a mechanism for this: Testcases. As you'll learn in the next tutorial.