Writing expressions

Using an expression in a step condition

You can use an expression in a step condition if you want to condition a step on the result of a calculation based on information you have gathered during the conversation.

For example, suppose a customer has $200 in a savings account and wants to transfer $150 from it to a new checking account. The funds transfer fee is $3, and the bank charges a fee when a savings account contains less than $50. You could create a step with a step condition that checks for this situation. The step condition would use an expression like this:

${savings} - (${Step_232} + ${transfer_fee}) < 50

where:

• ${savings} represents a session variable that stores the customer's savings account total.
• ${Step_232} represents the step that asks for the amount the customer wants to transfer.
• ${transfer_fee} represents a session variable that specifies the fee for a funds transfer.

If the step condition is met, the step warns the user that the requested transfer will bring the savings account balance below the $50 minimum and incur a fee, and ask to confirm before proceeding.

To use an expression in a step condition, follow these steps:

1. From the step, click Add condition.

   A condition is generated automatically with the most likely choice, which is typically any variables that were set in the previous step.

2. Click the first segment of the generated condition, and then scroll down and click Expression.

3. Optional: Click the Expand icon to open the expression editor window. (You can also type the expression directly in the field without opening the window, but the editor makes it easier to edit a longer or more complex expression.)

4. Type the expression that you want to use.

Using an expression to assign a value to a session variable

You can use an expression when assigning a value to a session variable if you want the variable's value to be calculated based on other variables.

For example, suppose you want to tell your customer the total cost of a purchase, including 6% sales tax and a flat $3.00 processing fee. To calculate the total cost, you could create a session variable and assign the value using an expression:

(${price} * 1.06) + 3

You can then reference this variable in the Assistant says field.

To use an expression when assigning a value to a session variable, follow these steps:

1. From within a step, click Set variable values.

2. Click Set new value.

3. From the drop-down list, select the session variable you want to store the value in.

4. After to, select Expression.

5. Type the expression you want to use.

6. If you are using the expression editor, click Apply to save your changes and close the editor window.

You can also use an expression to assign an initial value to a session variable. In the Session variable window, go to the Initial value field and click Use expression.

You can also write an expression directly without first picking a variable:

1. From within a step, click Set variable values.

2. Click Set new value.

3. From the drop-down list, select Expression.

4. Type the expression you want to use.

5. If you are using the expression editor, click Apply to save your changes and close the editor window.

Expression syntax

The watsonx Assistant expression language is based on the Spring Expression Language (SpEL), but with some important differences in syntax. For detailed background information about SpEL, see Spring Expression Language (SpEL).

{
  "name": {
    "firstname": "John",
    "lastname": "Doe"
  },
  "age": 36
}

{
  "temp_1": ${temp_1},
  "temp_2": ${temp_2},
  "avg_temp": (${temp_1} + ${temp_2}) / 2
}