Nested function in the context of ALGOL 60

⭐ Core Definition: 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++.

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👉 Nested function in the context of ALGOL 60

ALGOL 60 (short for Algorithmic Language 1960) is a member of the ALGOL family of computer programming languages. It followed on from ALGOL 58 which had introduced code blocks and the begin and end pairs for delimiting them, representing a key advance in the rise of structured programming. ALGOL 60 was one of the first languages implementing function definitions (that could be invoked recursively). ALGOL 60 function definitions could be nested within one another (a feature introduced by ALGOL 60) with lexical scope. It gave rise to many other languages, including CPL, PL/I, Simula, BCPL, B, Pascal, and C. Practically every computer of the era had a systems programming language based on ALGOL 60 concepts.

Niklaus Wirth based his own ALGOL W on ALGOL 60 before moving to develop Pascal. Algol-W was intended to be the next generation ALGOL but the ALGOL 68 committee decided on a design that was more complex and advanced rather than a cleaned simplified ALGOL 60. The official ALGOL versions are named after the year they were first published. ALGOL 68 is substantially different from ALGOL 60 and was criticised partially for being so, so that in general "ALGOL" refers to dialects of ALGOL 60.

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⭐ Core Definition: Nested function
👉 Nested function in the context of ALGOL 60
Nested function in the context of Automatic variable

Nested function in the context of Automatic variable

In computer programming, an automatic variable is a local variable which is allocated and deallocated automatically when program flow enters and leaves the variable's scope. The scope is the lexical context, particularly the function or block in which a variable is defined. Local data is typically (in most languages) invisible outside the function or lexical context where it is defined. Local data is also invisible and inaccessible to a called function, but is not deallocated, coming back in scope as the execution thread returns to the caller.

Automatic local variables primarily applies to recursive lexically scoped languages. Automatic local variables are normally allocated in the stack frame of the procedure in which they are declared. This was originally done to achieve re-entrancy and allowing recursion, a consideration that still applies today. The concept of automatic variables in recursive (and nested) functions in a lexically scoped language was introduced to the wider audience with ALGOL in the late 1950s, and further popularized by its many descendants.

View the full Wikipedia page for Automatic variable

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⭐ Core Definition: Nested function

👉 Nested function in the context of ALGOL 60

Nested function in the context of Automatic variable