Бағдарламалық кодтың лексикалық құрылымы: Блоктар

Lexical structure of source code grouped together

In computer programming, a block or code block or block of code is a lexical structure of source code which is grouped together. Blocks consist of one or more declarations and statements. A programming language that permits the creation of blocks, including blocks nested within other blocks, is called a block structured programming language. Blocks are fundamental to structured programming, where control structures are formed from blocks. Blocks have two functions: to group statements so that they can be treated as one statement, and to define scopes for names to distinguish them from the same name used elsewhere. In a block structured programming language, the objects named in outer blocks are visible inside inner blocks, unless they are masked by an object declared with the same name.

Ideas of block structure were developed in the 1950s during the development of the first autocodes, and were formalized in the Algol 58 and Algol 60 reports. Algol 58 introduced the notion of the "compound statement", which was related solely to control flow. The subsequent Revised Report which described the syntax and semantics of Algol 60 introduced the notion of a block and block scope, with a block consisting of " A sequence of declarations followed by a sequence of statements and enclosed between begin and end " in which "[e]very declaration appears in a block in this way and is valid only for that block."

Some languages which support blocks with declarations do not fully support all declarations; for instance many C derived languages do not permit a function definition within a block (nested functions). And unlike its ancestor Algol, Pascal does not support the use of blocks with their own declarations inside the begin and end of an existing block, only compound statements enabling sequences of statements to be grouped together in if, while, repeat and other control statements.

In some languages, a variable can be declared at function scope even within enclosed blocks. For example, in JavaScript, variables declared with var have function scope.