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Nested function
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Nested function
In computer programming, a nested function (or nested procedure or subroutine) is a named function that is defined within another, enclosing, block and is lexically scoped within the enclosing block – meaning it is only callable by name within the body of the enclosing block and can use identifiers declared in outer blocks, including outer functions. The enclosing block is typically, but not always, another function.
Programming language support for nested functions varies. With respect to structured programming languages, it is supported in some outdated languages such as ALGOL, Simula 67 and Pascal and in the commonly used JavaScript. It is commonly supported in dynamic and functional languages. However, it is not supported in some commonly used languages including standard C and C++.
Other programming technologies provide similar benefit. For example, a lambda function also allows for a function to be defined inside of a function (as well as elsewhere) and allows for similar data hiding and encapsulation. Notably, a lambda function has no name (is anonymous) and therefore cannot be called by name and has no visibility aspect.
The scope of a nested function is the block that contains it – be it a function block or block within a function body. It is not visible (cannot be called by name) outside its containing block.
A nested function can use identifiers (i.e. the name of functions, variables, types, classes) declared in any enclosing block, except when they are masked by inner declarations with the same names.
A nested function can be declared within a nested function, recursively, to form a deeply nested structure. A deeply nested function can access identifiers declared in all of its enclosing blocks, including enclosing functions.
Nested functions may in certain situations lead to the creation of a closure. If it is possible for the nested function to escape the enclosing function, for example if functions are first class objects and a nested function is passed to another function or returned from the enclosing function, then a closure is created and calls to this function can access the environment of the original function. The frame of the immediately enclosing function must continue to be alive until the last referencing closure dies and non-local automatic variables referenced in closures can therefore not be stack allocated in languages that allow the closure to persist beyond the lifetime of the enclosing block. This is known as the funarg problem and is a key reason why nested functions was not implemented in some simpler languages as it significantly complicates code generation and analysis, especially when functions are nested to various levels, sharing different parts of their environment.
The nested function technology allows a programmer to write source code that includes beneficial attributes such as information hiding, encapsulation and decomposition. The programmer can divide a task into subtasks which are only meaningful within the context of the task such that the subtask functions are hidden from callers that are not designed to use them.
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Nested function AI simulator
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Nested function
In computer programming, a nested function (or nested procedure or subroutine) is a named function that is defined within another, enclosing, block and is lexically scoped within the enclosing block – meaning it is only callable by name within the body of the enclosing block and can use identifiers declared in outer blocks, including outer functions. The enclosing block is typically, but not always, another function.
Programming language support for nested functions varies. With respect to structured programming languages, it is supported in some outdated languages such as ALGOL, Simula 67 and Pascal and in the commonly used JavaScript. It is commonly supported in dynamic and functional languages. However, it is not supported in some commonly used languages including standard C and C++.
Other programming technologies provide similar benefit. For example, a lambda function also allows for a function to be defined inside of a function (as well as elsewhere) and allows for similar data hiding and encapsulation. Notably, a lambda function has no name (is anonymous) and therefore cannot be called by name and has no visibility aspect.
The scope of a nested function is the block that contains it – be it a function block or block within a function body. It is not visible (cannot be called by name) outside its containing block.
A nested function can use identifiers (i.e. the name of functions, variables, types, classes) declared in any enclosing block, except when they are masked by inner declarations with the same names.
A nested function can be declared within a nested function, recursively, to form a deeply nested structure. A deeply nested function can access identifiers declared in all of its enclosing blocks, including enclosing functions.
Nested functions may in certain situations lead to the creation of a closure. If it is possible for the nested function to escape the enclosing function, for example if functions are first class objects and a nested function is passed to another function or returned from the enclosing function, then a closure is created and calls to this function can access the environment of the original function. The frame of the immediately enclosing function must continue to be alive until the last referencing closure dies and non-local automatic variables referenced in closures can therefore not be stack allocated in languages that allow the closure to persist beyond the lifetime of the enclosing block. This is known as the funarg problem and is a key reason why nested functions was not implemented in some simpler languages as it significantly complicates code generation and analysis, especially when functions are nested to various levels, sharing different parts of their environment.
The nested function technology allows a programmer to write source code that includes beneficial attributes such as information hiding, encapsulation and decomposition. The programmer can divide a task into subtasks which are only meaningful within the context of the task such that the subtask functions are hidden from callers that are not designed to use them.