quine 音标拼音: [kw'ɑɪn]
Quine n 1 :
United States philosopher and logician who championed an empirical view of knowledge that depended on language (
1908 -
2001 ) [
synonym : {
Quine }, {
W .
V .
Quine }, {
Willard Van Orman Quine }]
/kwi :n / (After the logician Willard V . Quine ,
via Douglas Hofstadter ) A program that generates a copy of its
own source text as its complete output . Devising the shortest
possible quine in some given programming language is a common
hackish amusement .
In most interpreted languages , any constant , e .g . 42 , is a
quine because it "evaluates to itself ". In certain {Lisp }
dialects (e .g . {Emacs Lisp }), the symbols "nil " and "t " are
self -quoting ", i .e . they are both a symbol and also the value
of that symbol . In some dialects , the function -forming
function symbol , "lambda " is self -quoting so that , when
applied to some arguments , it returns itself applied to those
arguments . Here is a quine in {Lisp } using this idea :
lambda (x ) (list x x )) (lambda (x ) (list x x )))
Compare this to the {lambda expression }:
x . x x ) (\ x . x x )
which reproduces itself after one step of {beta reduction }.
This is simply the result of applying the {combinator } {fix }
to the {identity function }. In fact any quine can be
considered as a {fixed point } of the language 's evaluation
mechanism .
We can write this in {Lisp }:
lambda (x ) (funcall x x )) (lambda (x ) (funcall x x )))
where "funcall " applies its first argument to the rest of its
arguments , but evaluation of this expression will never
terminate so it cannot be called a quine .
Here is a more complex version of the above Lisp quine , which
will work in Scheme and other Lisps where "lambda " is not
self -quoting :
lambda (x )
list x (list (quote quote ) x )))
quote
lambda (x )
list x (list (quote quote ) x )))))
It 's relatively easy to write quines in other languages such
as {PostScript } which readily handle programs as data ; much
harder (and thus more challenging !) in languages like {C }
which do not . Here is a classic {C } quine for {ASCII }
machines :
char *f ="char *f =%c %s %c ;main () {printf (f ,34 ,f ,34 ,10 );}%c ";
main (){printf (f ,34 ,f ,34 ,10 );}
For excruciatingly exact quinishness , remove the interior line
break . Some infamous {Obfuscated C Contest } entries have been
quines that reproduced in exotic ways .
Ken Thompson }'s {back door } involved an interesting variant
of a quine - a compiler which reproduced part of itself when
compiling (a version of ) itself .
Jargon File }]
1995 -04 -25 )
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