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JavaSucksMan (talk | contribs) →Syntax: added Haskell to offside rule |
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==History==
Ideas of block structure were developed in the 1950s during the development of the first [[autocode]]s, 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]].<ref name="algol58_report">{{cite journal
|last1= Perlis |first1 = A. J. |author-link1=Alan
|last2= Samelson |first2= K.
| date = 1958
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==Syntax==
Blocks use different syntax in different languages.
* the [[ALGOL]] family in which blocks are delimited by the keywords "<code>begin</code>" and "<code>end</code>" or equivalent. In [[C (programming language)|C]], blocks are delimited by curly braces - "<code>{</code>" and "<code>}</code>". [[ALGOL 68]] uses parentheses.
* Parentheses - "<code>(</code>" and "<code>)</code>", are used in the MS-DOS [[batch language]]
* [[off-side rule|indentation]], as in [[Python (programming language)|Python]] and [[Haskell]]
* [[s-expression]]s with a syntactic keyword such as <code>prog</code> or <code>let</code> (as in the [[Lisp (programming language)|Lisp]] family)
* In 1968 (with [[ALGOL 68]]), then in [[Edsger W. Dijkstra]]'s 1974 [[Guarded Command Language#Selection: if|Guarded Command Language]] the conditional and iterative code block are alternatively terminated with the block reserved word ''reversed'': e.g. <code><u>'''if'''</u> ~ <u>then</u> ~ <u>elif</u> ~ <u>else</u> ~ <u>'''fi'''</u></code>, <code><u>'''case'''</u> ~ <u>in</u> ~ <u>out</u> ~ <u>'''esac'''</u></code> and <code><u>for</u> ~ <u>while</u> ~ <u>'''do'''</u> ~ <u>'''od'''</u></code>
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The semantic meaning of a block is twofold. Firstly, it provides the programmer with a way for creating arbitrarily large and complex structures that can be treated as units. Secondly, it enables the programmer to limit the scope of variables and sometimes other objects that have been declared.
In early languages such as [[Fortran IV]] and [[BASIC]], there were no statement blocks or control structures other than simple forms of loops. Conditionals were implemented using conditional [[goto]] statements:
<syntaxhighlight lang="fortranfixed">
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