The precise definition of a functional programming language is often a hotly debated topic among computer scientists, but it is generally accepted that such languages emphasize the value of expressions, rather than the execution of commands. These languages enable the programmer to think like a mathematician by emphasizing data over state. Functional programming techniques (and the supporting languages, e.g., LISP) have existed virtually since the dawn of computer science, but they have been largely overshadowed by imperative languages (e.g., C/C++) within mainstream IT efforts in recent decades. Functional programming has been successfully leveraged in specialized fields for many years—for example, in academia, science and engineering, financial calculation engines, artificial intelligence and development tools.