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A fundamental distinction in scope is what "part of a program" means. In languages with lexical scope (also called static scope), name resolution depends on the location in the source code and the lexical context (also called static context), which is defined by where the named variable or function is defined.
However, static typing does imply static name resolution. Static name resolution catches, at compile time, use of variables that are not in scope; preventing programmer errors. Languages with dynamic scope resolution sacrifice this safety for more flexibility; they can typically set and get variables in the same scope at runtime.
Function bindings cannot be dynamically scoped using flet (which only provides lexically scoped function bindings), but function objects (a first-level object in Common Lisp) can be assigned to dynamically scoped variables, bound using let in dynamic scope, then called using funcall or APPLY.
Local variables may have a lexical or dynamic scope, though lexical (static) scoping is far more common.In lexical scoping (or lexical scope; also called static scoping or static scope), if a variable name's scope is a certain block, then its scope is the program text of the block definition: within that block's text, the variable name exists, and is bound to the variable's value, but outside ...
Dynamic binding (or late binding or virtual binding) is name binding performed as the program is running. [2] An example of a static binding is a direct C function call: the function referenced by the identifier cannot change at runtime. An example of dynamic binding is dynamic dispatch, as in a C++ virtual method call.
The term closure is often used as a synonym for anonymous function, though strictly, an anonymous function is a function literal without a name, while a closure is an instance of a function, a value, whose non-local variables have been bound either to values or to storage locations (depending on the language; see the lexical environment section below).
The name dynamic binding is sometimes used, [2] but is more commonly used to refer to dynamic scope. With early binding, or static binding, in an object-oriented language, the compilation phase fixes all types of variables and expressions. This is usually stored in the compiled program as an offset in a virtual method table ("v-table"). [3]
A prominent characteristic of Emacs Lisp is in its use of dynamic rather than lexical scope by default. That is, a function may reference local variables in the scope it is called from, but not in the scope where it was defined. Recently, there has been an ongoing effort to update code to use lexical scoping, for reasons outlined below.