# Expressions ### **Introduction to Open Loyalty Language** \ When setting up conditions and effects for rules in [Campaigns](https://help.openloyalty.io/campaigns), you may find that some situations are not covered by premade values. However, you are not limited to using these values - you can use an Open Loyalty language to create very specific conditions and values. \ \ In conditions, you can find a condition called **Expressions**.

You can set the value of such an expression. It can be set as a combination of attributes and operators using the meta language created by Open Loyalty. It allows you to create a fully customizable condition that meets the rules of your planned loyalty program. For example, you can create a campaign that is triggered when a customer buys a product from a certain category. You can do it in two ways: Set a premade condition:

Or use an expression:

In the same way, you can create custom campaign effects - you can use premade values, or enter them yourself:

In this section, you will find a description of the meta-language together with all the supported syntaxes, which is based on the expression syntax of Symfony Expression. *** #### **The component supports** * strings - single and double quotes (e.g. 'hello') * numbers - integers (e.g. 103), decimals (e.g. 9.95), decimals without leading zeros (e.g. .99, equivalent to 0.99); all numbers support optional underscores as separators to improve readability (e.g. 1\_000\_000, 3.14159\_26535) * arrays - using JSON-like notation (e.g. \[1, 2]) * hashes - using JSON-like notation (e.g. { foo: 'bar' }) * booleans - true and false * null - null * exponential - also known as scientific (e.g. 1.99E+3 or 1e-2)