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In computer programming, indentation style is a convention, a.k.a. style, governing the indentation of blocks of source code.An indentation style generally involves consistent width of whitespace (indentation size) before each line of a block, so that the lines of code appear to be related, and dictates whether to use space or tab characters for the indentation whitespace.
Different programmers often prefer different styles of formatting, such as the use of code indentation and whitespace or positioning of braces. A code formatter or code indenter converts source code from one format style to another. This is relatively straightforward because of the unambiguous syntax of programming languages.
Indentation style can assist a reader in various way including: identifying control flow and blocks of code. In some programming languages, indentation is used to delimit blocks of code and therefore is not matter of style. In languages that ignore whitespace, indentation can affect readability. For example, formatted in a commonly-used style:
The rules a compiler applies to the source creates implicit standards. For example, Python code is much more consistently indented than, say Perl, because whitespace (indentation) is actually significant to the interpreter. Python does not use the brace syntax Perl uses to delimit functions. Changes in indentation serve as the delimiters.
Indentation is essentially the same regardless of whether the writing system is left-to-right (e.g. Latin and Cyrillic) or right-to-left (e.g. Hebrew and Arabic) when considering line beginning and end. For example, indenting at the beginning of line means on the left for a left-to-right script and on the right for right-to-left script.
Java compilers do not enforce these rules, but failing to follow them may result in confusion and erroneous code. For example, widget.expand() and Widget.expand() imply significantly different behaviours: widget.expand() implies an invocation to method expand() in an instance named widget , whereas Widget.expand() implies an invocation to ...
This ensures that the line of tokens conform to the formal grammars of the programming language. The parsing stage itself can be divided into two parts: the parse tree , or "concrete syntax tree", which is determined by the grammar, but is generally far too detailed for practical use, and the abstract syntax tree (AST), which simplifies this ...
Fortran 90 removed the need for the indentation rule and added line comments, using the ! character as the comment delimiter. COBOL. In fixed format code, line indentation is significant. Columns 1–6 and columns from 73 onwards are ignored. If a * or / is in column 7, then that line is a comment.