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In [[Prolog (programming language)|Prolog]], symbols (or atoms) are the primary primitive data types, similar to numbers.<ref name=Bratko2001>{{Cite book | last1 = Bratko | first1 = Ivan | title = Prolog programming for artificial intelligence | year = 2001 | publisher = Addison Wesley | ___location = Harlow, England ; New York | isbn = 0-201-40375-7 | pages = }}</ref> The exact notation may differ in different [[Prolog (programming language)|Prolog]]'s dialects. However, it is always quite simple (no quotations or special beginning characters are necessary).
Contrary to other languages, it is possible to give symbols some ''meaning'' by creating some [[Prolog (
====Examples====
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===Ruby===
In [[Ruby (programming language)|Ruby]], symbols can be created with a literal form, or by converting a string.<ref name=pickaxe />
They can be used as an identifier or an interned string.<ref name="rubysymbol">{{cite web|last=Kidd|first=Eric|title=13 Ways of Looking at a Ruby Symbol|url=http://www.randomhacks.net/articles/2007/01/20/13-ways-of-looking-at-a-ruby-symbol#9|work=Random Hacks|accessdate=10 July 2011}}</ref> Two symbols with the same contents will always refer to the same object.<ref>http://www.ruby-doc.org/docs/ProgrammingRuby/html/language.html#UI</ref>
It is considered a [[best practice]] to use symbols as keys to an [[associative array]] in Ruby.<ref name=rubysymbol /><ref name="wrongreason">{{cite web|title=Using Symbols for the Wrong Reason|url=http://microjet.ath.cx/WebWiki/2005.12.27_UsingSymbolsForTheWrongReason.html|work=Gnomic Notes}}</ref>
====Examples====
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my_string = :hello.to_s
</source>
Symbols are objects of the <code>Symbol</code> class in Ruby:<ref name="rdocsymbol">{{cite web|title=Symbol|url=http://www.ruby-doc.org/core/classes/Symbol.html|work=Ruby Documentation|accessdate=10 July 2011}}</ref>
<source lang=ruby>
my_symbol = :hello_world
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