Lexical scope

Lexical scope

With lexical scope, a name always refers to its lexical context. This is a property of the program text and is made independent of the runtime call stack by the language implementation. Because this matching only requires analysis of the static program text, this type of scope is also called static scope. Lexical scope is standard in all ALGOL-based languages such as Pascal, Modula-2, and Ada, and in modern functional languages such as ML and Haskell. It is also used in the C language and its syntactic and semantic relatives, although with different kinds of limitations. Static scope allows the programmer to reason about object references such as parameters, variables, constants, types, functions, etc., as simple name substitutions. This makes it much easier to make modular code and reason about it, since the local naming structure can be understood in isolation. In contrast, dynamic scope forces the programmer to anticipate all possible execution contexts in which the module's code may be invoked.