====AQL Language Introduction====

The ARDI Query Language is a simple [[https://en.wikipedia.org/wiki/Concatenative_programming_language|concatenative language]].

It allows you to write your queries as 'programs' that run to produce the results you need.

For those used to traditional languages, the biggest difference is that **the parameters to a function appear //before// the function**.

For example, the **ASSET** function searches ARDI for assets that match a given piece of text (ie. it searches for a name or ID number).

The correct AQL to find the asset is...

    'Wind Turbine' ASSET

===Tokens===

A //token// is a single piece of your query. For example, there were two tokens in the query above 

^Tokens^Type^
|'Wind Turbine'|[[CONSTLIST]]|
|ASSET|[[FUNCTION]]|

Each token has a //type//. Normally these will be either **functions** (commands to be run) or **lists**. 

Whenever a single item that isn't a function appears, it is converted into a list that contains just the one item (ie. a list of constant values with only one item - the string 'Wind Turbine').

===The Stack===

Each token of your AQL query is added to what is called the STACK. The stack is simply a list of tokens waiting to be processed.

The stack is processed from the left to the right. When a FUNCTION is found, it takes any parameters it needs off the stack and optionally writes tokens back onto the stack when it's done.

For example, the **ASSET** function takes a single parameter - a [[CONSTLIST]]. It then returns a [[ASSETLIST]] containing all of the assets it could find that had could be found with a name or properties that matched //any one of the values in the parameter//.

===Multiple Items in a List===

If there is more than one item in a list, the system adds the various results together. For example...

    ('Wind Turbine #1','Wind Turbine #2') ASSET

The brackets make AQL copy the two strings into the same CONSTLIST, resulting in...

^Tokens^Type^
|'Wind Turbine #1' + 'Wind Turbine #2'|[[CONSTLIST]]|
|ASSET|[[FUNCTION]]|

In this case, **ASSET** would return a list of two assets - Turbine #1 and Turbine #2.

If you're curious, you can read the [[aql:aql_reference_-_alphabetical|Alphabetical List of AQL Functions]].

===Continue Reading===

[[Example AQL Statements]]