Dynamic programming language

Dynamic programming language, in computer science, is a class of high-level programming languages which, at runtime, execute many common programming behaviors that static programming languages perform during compilation. These behaviors could include extension of the program, by adding new code, by extending objects and definitions, or by modifying the type system. Although similar behaviours can be emulated in nearly any language, with varying degrees of difficulty, complexity and performance costs, dynamic languages provide direct tools to make use of them. Many of these features were first implemented as native features in the Lisp programming language.

Most dynamic languages are also dynamically typed, but not all are. Dynamic languages are frequently (but not always) referred to as "scripting languages", although the term "scripting language" in its narrowest sense refers to languages specific to a given run-time environment.

Some dynamic languages offer an eval function. This function takes a string parameter containing code in the language, and executes it. If this code stands for an expression, the resulting value is returned. However, Erik Meijer and Peter Drayton suggest that programmers "use eval as a poor man's substitute for higher-order functions."

A type or object system can typically be modified during runtime in a dynamic language. This can mean generating new objects from a runtime definition or based on mixins of existing types or objects. This can also refer to changing the inheritance or type tree, and thus altering the way that existing types behave (especially with respect to the invocation of methods).

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