Although LINGO has a convenient, interactive interface and a large library of callable functions that make it easy to set up and solve models, there may be times when you would like to bundle LINGO's functionality into your own applications, or call functions from within your LINGO models that were written in an external programming language. LINGO makes use of the Dynamic Link Library (DLL) standard under Windows to provide you with a "hook" to access LINGO's functionality from within your own custom applications. This gives you the ability to build application specific front-ends to LINGO that allow naïve users to input data and view solutions in a simple, familiar way without having to worry about the details of LINGO modeling. Your application handles the details of driving LINGO in the background, invisible to the user. LINGO also allows you to provide custom functions in the DLL format that you can call from within any model with the @USER function.

In the following section, The LINGO Dynamic Link Library, we document how to call the LINGO DLL in order to add LINGO's functionality to your own applications. Following this, in the User Defined Functions section, we will show you how to build a function in an external programming language and call it from a LINGO model with the @USER function.