Metasyntactic variable

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A metasyntactic variable, in computer science, is a placeholder name or an alias term commonly used to denote an arbitrary thing, or an arbitrary member of a class of things under discussion. The use of a metasyntactic variable is helpful in freeing a programmer from creating a logically named variable, which is often useful when creating or teaching examples of an algorithm. The word foo is the principal example.^[1]

The term "metasyntactic variable" is primarily found in informal literature. It is sometimes also used as a synonym for metavariable.

Any symbol or word which does not violate the rules of the language can be used as a metasyntactic variable, but nonsense words are commonly used. The same concept is employed in other fields where it is expressed by terms such as schematic variable (see logical form).

By mathematical analogy: A metasyntactic variable is a word that is a variable for other words, just as in algebra letters are used as variables for numbers.^[1]

Construction

• meta- means providing information about, or transcending,
• syntax denotes the grammatical arrangement of words or the grammatical rules of a programming language, and
• a variable is something that can assume a value, or something likely to vary.

So metasyntactic variable denotes a word that "transcends grammar and can assume a value" or one that is "more comprehensive than suggested by its grammatical arrangement and is likely to vary". It may also denote a word that provides information about the grammatical arrangement of words by being able to assume a value that is expected to vary.

Words commonly used as metasyntactic variables

English

A "standard list of metasyntactic variables used in syntax examples" often used in the United States is: foo, bar, baz, qux, quux, corge, grault, garply, waldo, fred, plugh, xyzzy, thud.^[1] The word foo occurs in over 330 RFCs and bar occurs in over 290.^[2] Wibble, wobble, wubble, Fred and flob are often used in the UK.^[3]

Due to English being the foundation-language, or lingua franca, of most computer programming languages these variables are also commonly seen even in programs and examples of programs written for other spoken-language audiences.

French

In French, the words toto, titi, tata and tutu are commonly used.

Japanese

In Japanese, the words hoge and page are commonly used, with other common words and variants being piyo, fuga, hogera, and hogehoge.^[4] Note that -ra is a pluralizing ending in Japanese, and reduplication is also used for pluralizing. The origin of hoge as a metasyntactic variable is not known, but it is believed to date to the early 1980s.^[4]

Israeli Hebrew

In Hebrew, the words chupchick and stam are commonly used.

Italian

In Italian, the word pippo is commonly used. Strangely enough, besides being an abbreviation of the first names Giuseppe (Joseph) and Filippo (Philip), pippo is the Italian name of the Disney character Goofy, but it is probably used just because of its sound which is quite strange; moreover, this name is very fast to be typed with the computer keyboard, as it involves three near keys (P, I and O). Sometimes the words pluto and paperino (Italian name of Donald Duck) can be hence used as additional terms.

Portuguese

In Portuguese, the words fulano, cicrano and beltrano are commonly used. These words have the constraint that they can only be used to refer to people.

Spanish

In Spanish, the words fulano, mengano and zutano are commonly used, often followed by de tal mocking a lastname in Spanish form (i.e. Fulano de Tal). These words have the constraint that they can only be used to refer to people, as in the case with Portuguese. Also, when referring to an example of some person performing a certain action, Perico de los Palotes can also be used as a placeholder for a real name. In place of people or objects (including numbers, etc.) the usual X, Y, Z are used (i.e. Person X, Quantity X).

Programming language examples

C

In the following example of the C programming language the function name foo and the variable name bar are both metasyntactic variables. Lines beginning with /* and ending 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;
}

Python

Spam, ham, and eggs are the principal metasyntactic variables used in the Python programming language.^[5] This is a reference to the famous comedy sketch Spam by Monty Python, the eponym of the language.^[6] In the following example spam, ham, and eggs are metasyntactic variables and lines beginning with # are comments.

# Define a function named spam
def spam():
 
    # define the variable ham
    ham = "Hello World!"
 
    #define the variable eggs
    eggs = 1
 
    return

Ruby

In the following example the foo, bar, and baz are metasyntactic variables and lines beginning with # are comments.

# Declare the variable foo and set equal to 1
foo = 1
 
# Declare the variable bar and set equal to 2
bar = 2
 
# Declare the method (function) named baz, which prints the text 'Hello world'
def baz
   puts 'Hello world'
end

See also

• Metavariable (logic)
• English in computing
• Non-English-based programming languages
• Alice and Bob
• John Doe
• Fnord
• Free variables and bound variables
• Gadget
• Hello World
• Lorem Ipsum
• Nonce word
• Placeholder name
• Widget

References

External links

• Definition of metasyntactic variable, with examples.
• Examples of metasyntactic variables used in Commonwealth Hackish, such as wombat.
• Variable "foo" and Other Programming Oddities