Metasyntactic variable

Since English is the foundation language or lingua franca of most computer programming languages, variables that originate in English are commonly seen even in programs and examples of programs written for other spoken-language audiences.

The variables used in a particular context may depend on subcultures that develop around programming languages.

Metasyntactic variables used commonly across all programming languages include foobar, foo, bar, baz, {{not a typo|qux}}, {{not a typo|quux}}, {{not a typo|corge}}, {{not a typo|grault}}, {{not a typo|garply}}, {{not a typo|waldo}}, {{not a typo|fred}}, {{not a typo|plugh}}, xyzzy (computing), and thud.{{cite mailing list|title=Metasyntactic variable|first=Stuart|last=Laughlin|date=November 18, 2016|access-date=November 18, 2016|url=https://www.progclub.org/pipermail/programming/2016-November/002305.html|mailing-list=programming@ProgClub|url-status=dead|archive-url=https://web.archive.org/web/20221202085628/https://www.progclub.org/pipermail/programming/2016-November/002305.html|archive-date=December 2, 2022}} Two of these words, plugh and xyzzy, are taken from the game Colossal Cave Adventure.{{cite web |url=https://jerz.setonhill.edu/if/crowther/advdat.77-03-11 |title=advdat.77-03-11 |last=Crowther |first=Will |date=1977-03-11 |website= Colossal Cave Adventure Source Code |publisher=Dennis G. Jerz |access-date=2024-02-28}}

A fuller reference can be found in The Hacker's Dictionary from MIT Press.

In Japanese, the words {{Transliteration|ja|hoge}} (ほげ){{Cite web|url=https://ejje.weblio.jp/content/hoge|title=hogeの意味・使い方 - 英和辞典 Weblio 辞書|website=ejje.weblio.jp}} and {{Transliteration|ja|fuga}} (ふが) are commonly used, with other common words and variants being {{Transliteration|ja|piyo}} (ぴよ), {{Transliteration|ja|hogera}} (ほげら), and {{Transliteration|ja|hogehoge}} (ほげほげ).メタ構文変数 {{in lang|ja}}{{Circular reference|date=September 2017}} The origin of {{Transliteration|ja|hoge}} as a metasyntactic variable is not known, but it is believed to date to the early 1980s.

In France, the word toto is widely used, with variants tata, titi, tutu as related placeholders. One commonly-raised source for the use of toto is a reference to the stock character used to tell jokes with Tête à Toto.{{Citation needed|date=February 2022}}

In Turkey, the words hede and hödö (usually spelt hodo due to ASCII-only naming constraints of programming languages) are well-known metasyntactic variables that stem from popular humorous cartoon magazines of the 90's like LeMan. The words do not mean anything, and are used for precisely that reason. The terms were popularized more widely by the actor and stand-up comedian Cem Yılmaz in the late 90's and early 2000's.{{Cite book |url=https://books.google.com/books?id=dRxdDwAAQBAJ&dq=hede+h%C3%B6d%C3%B6&pg=PA12 |title=LeMan Dergisi 1376. Sayı |publisher=Lm Basin Yayin Ltd.şti. |language=tr}}

In Italian software programming culture, it is common to encounter names of Walt Disney characters (as found in the Italian versions of the shows) being used as variables. These names often appear in pseudo-code, are referenced in software engineering classes, and are commonly employed when explaining algorithms to colleagues. Among the most frequently used are "pippo" (Goofy), "pluto," and "paperino" (Donald Duck).{{Cite web|url=http://www.catb.org/jargon/html/M/metasyntactic-variable.html|title=The Jargon File - metasyntactic variable|website=www.catb.org/}}

File:Metasyntactic Variable FOO in Shell.png

{{See also|C programming language}}

In the following example the function name foo and the variable name bar are both metasyntactic variables. Lines beginning with // are comments.

// The function named foo

int foo(void)

{

// Declare the variable bar and set the value to 1

int bar = 1;

return bar;

}

{{See also|C++}}

Function prototypes with examples of different argument passing mechanisms:{{cite book|first1=John|last1=Mongan|first2=Noah|last2=Kindler|first3=Eric|last3=Giguere|title=Programming Interviews Exposed: Secrets to Landing Your Next Job|url=https://books.google.com/books?id=GQE4r2e5fAsC&pg=PA242|year=2012|publisher=John Wiley & Sons|isbn=978-1-118-28720-0|page=242}}

void Foo(Fruit bar);

void Foo(Fruit* bar);

void Foo(const Fruit& bar);

Example showing the function overloading capabilities of the C++ language

void Foo(int bar);

void Foo(int bar, int baz);

void Foo(int bar, int baz, int qux);

Spam, ham, and eggs are the principal metasyntactic variables used in the Python programming language.{{Cite web|url=https://docs.python.org/3/tutorial/|title=The Python Tutorial — Python 3.8.1 documentation|website=docs.python.org}} This is a reference to the famous comedy sketch, "Spam", by Monty Python, the eponym of the language.{{Cite web |date=2021-09-04 |title=General Python FAQ — Python 3.9.7 documentation |url=https://docs.python.org/3/faq/general.html |url-status=live |archive-url=https://web.archive.org/web/20210826153036/https://docs.python.org/3/faq/general.html#why-is-it-called-python |archive-date=2021-08-26 |access-date=2021-09-05 |website=docs.python.org |publisher=Python Software Foundation |at=Why is it called Python?}}

In the following example spam, ham, and eggs are metasyntactic variables and lines beginning with # are comments.

1. Define a function named spam

def spam():

# Define the variable ham

ham = "Hello World!"

# Define the variable eggs

eggs = 1

return

Both the IETF RFCs and computer programming languages are rendered in plain text, making it necessary to distinguish metasyntactic variables by a naming convention, since it would not be obvious from context.

Here is an example from the official IETF document explaining the e-mail protocols (from RFC 772 - cited in RFC 3092):

All is well; now the recipients can be specified.

S: MRCP TO:

R: 200 OK

S: MRCP TO:

R: 553 No such user here

S: MRCP TO:

R: 200 OK

S: MRCP TO:<@Y,@X,fubar@Z>

R: 200 OK

Note that the failure of "Raboof" has no effect on the storage of

mail for "Foo", "bar" or the mail to be forwarded to "fubar@Z"

through host "X".

(The documentation for texinfo emphasizes the distinction between metavariables and mere variables used in a programming language being documented in some texinfo file as: "Use the @var command to indicate metasyntactic variables. A metasyntactic variable is something that stands for another piece of text. For example, you should use a metasyntactic variable in the documentation of a function to describe the arguments that are passed to that function. Do not use @var for the names of particular variables in programming languages. These are specific names from a program, so @code is correct for them."{{cite web |url=http://sunsite.ualberta.ca/Documentation/Gnu/texinfo-4.0/html_chapter/texinfo_10.html |title=Marking Words and Phrases |work=Texinfo 4.0. The GNU Documentation Format|access-date=2012-11-25 |url-status=dead |archive-url=https://web.archive.org/web/20091106004856/http://sunsite.ualberta.ca/Documentation/Gnu/texinfo-4.0/html_chapter/texinfo_10.html |archive-date=2009-11-06 }})

Another point reflected in the above example is the convention that a metavariable is to be uniformly substituted with the same instance in all its appearances in a given schema. This is in contrast with nonterminal symbols in formal grammars where the nonterminals on the right of a production can be substituted by different instances.{{cite book|author=R. D. Tennent|title=Specifying Software: A Hands-On Introduction|year=2002|publisher=Cambridge University Press|isbn=978-0-521-00401-5|pages=36–37 and 210}}

It is common to use the name ACME in example SQL databases and as a placeholder company-name for the purpose of teaching. The term 'ACME Database' is commonly used to mean a training or example-only set of database data used solely for training or testing.

ACME is also commonly used in documentation which shows SQL usage examples, a common practice with in many educational texts as well as technical documentation from companies such as Microsoft and Oracle.{{cite book | last=Kriegel | first=Alex | title=SQL bible | publisher=Wiley | publication-place=Indianapolis, Ind | year=2008 | isbn=978-0-470-22906-4 | oclc=402446308 }}{{cite book | last=Ruel | first=Chris | title=Oracle 12c for dummies | publisher=John Wiley & Sons | publication-place=Hoboken, NJ | year=2014 | isbn=978-1-118-74531-1 | oclc=870334544 | language=da }}{{Cite web|url=https://docs.microsoft.com/en-us/dotnet/architecture/modern-web-apps-azure/work-with-data-in-asp-net-core-apps|title=Work with data in ASP.NET Core Apps|website=docs.microsoft.com|date=25 April 2023 }}

• Metavariable (logic)
• xyzzy
• Alice and Bob
• John Doe
• Fnord
• Free variables and bound variables
• Gadget
• Lorem ipsum
• Nonce word
• Placeholder name
• Widget
• Smurf

{{Reflist}}

• [http://www.catb.org/jargon/html/M/metasyntactic-variable.html Definition of metasyntactic variable, with examples.]
• [http://www.catb.org/jargon/html/C/Commonwealth-Hackish.html Examples of metasyntactic variables] used in Commonwealth Hackish, such as wombat.
• [http://blog.codinghorror.com/variable-foo-and-other-programming-oddities/ Variable "foo" and Other Programming Oddities]

Category:Placeholder names

Category:Metalogic

Category:Variable (computer science)

Category:Syntax (logic)