2014-04-26 10:52:28 -04:00
|
|
|
BNF
|
|
|
|
|
|
2014-04-26 11:54:15 -04:00
|
|
|
/BNF/ , n. 1. [techspeak] Acronym for Backus Normal Form (later retronymed
|
|
|
|
|
to Backus-Naur Form because BNF was not in fact a normal form), a
|
|
|
|
|
metasyntactic notation used to specify the syntax of programming languages,
|
|
|
|
|
command sets, and the like. Widely used for language descriptions but seldom
|
|
|
|
|
documented anywhere, so that it must usually be learned by osmosis from
|
|
|
|
|
other hackers. Consider this BNF for a U.S. postal address: postal-address
|
|
|
|
|
::= name-part street-address zip-part personal-part ::= name | initial .
|
|
|
|
|
name-part ::= personal-part last-name [ jr-part ] EOL | personal-part
|
|
|
|
|
name-part street-address ::=[ apt ] house-num street-name EOL zip-part
|
|
|
|
|
::= town-name , state-code ZIP-code EOL This translates into English as:
|
|
|
|
|
A postal-address consists of a name-part, followed by a street-address part,
|
|
|
|
|
followed by a zip-code part. A personal-part consists of either a first name
|
|
|
|
|
or an initial followed by a dot. A name-part consists of either: a
|
|
|
|
|
personal-part followed by a last name followed by an optional jr-part (Jr.,
|
|
|
|
|
Sr., or dynastic number) and end-of-line, or a personal part followed by a
|
|
|
|
|
name part (this rule illustrates the use of recursion in BNFs, covering the
|
|
|
|
|
case of people who use multiple first and middle names and/or initials). A
|
|
|
|
|
street address consists of an optional apartment specifier, followed by a
|
|
|
|
|
street number, followed by a street name. A zip-part consists of a
|
|
|
|
|
town-name, followed by a comma, followed by a state code, followed by a
|
|
|
|
|
ZIP-code followed by an end-of-line. Note that many things (such as the
|
|
|
|
|
format of a personal-part, apartment specifier, or ZIP-code) are left
|
|
|
|
|
unspecified. These are presumed to be obvious from context or detailed
|
|
|
|
|
somewhere nearby. See also parse. 2. Any of a number of variants and
|
|
|
|
|
extensions of BNF proper, possibly containing some or all of the regexp
|
|
|
|
|
wildcards such as * or +. In fact the example above isn't the pure form
|
|
|
|
|
invented for the Algol-60 report; it uses [] , which was introduced a few
|
|
|
|
|
years later in IBM's PL/I definition but is now universally recognized. 3.
|
|
|
|
|
In science-fiction fandom , a Big-Name Fan (someone famous or notorious).
|
|
|
|
|
Years ago a fan started handing out black-on-green BNF buttons at SF
|
|
|
|
|
conventions; this confused the hacker contingent terribly.
|
|
|
|
|
|
