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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 Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=Lisp">Lisp dialEcts (E.g. Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=Emacs Lisp">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 Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=Lisp">Lisp using this idEa: ((lambda (x) (list x x)) (lambda (x) (list x x))) ComparE this to thE Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=lambda ExprEssion">lambda ExprEssion: ( x . x x) ( x . x x) which rEproducEs itsElf aftEr onE stEp of Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=bEta rEduction">bEta rEduction. This is simply thE rEsult of applying thE Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=combinator">combinator Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=fix">fix to thE Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=idEntity function">idEntity function. In fact any quinE can bE considErEd as a Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=fixEd point">fixEd point of thE languagE' s Evaluation mEchanism. WE can writE this in Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=Lisp">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 Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=PostScript">PostScript which rEadily handlE programs as data much hardEr (and thus morE challEnging!) in languagEs likE Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=C">C which do not. HErE is a classic Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=C">C quinE for Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=ASCII">ASCII machinEs: char*f="char*f=%c%s%c main() Ef="f,34,f,34,10">printf%c" main()Ef="f,34,f,34,10">printf For Excruciatingly Exact quinishnEss, rEmovE thE intErior linE brEak. SomE infamous Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=ObfuscatEd C ContEst">ObfuscatEd C ContEst EntriEs havE bEEn quinEs that rEproducEd in Exotic ways. Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=KEn Thompson">KEn Thompson' s Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=back door">back door involvEd an intErEsting variant of a quinE - a compilEr which rEproducEd part of itsElf whEn compiling (a vErsion of) itsElf. [Ef="modulE.php?namE=LExikon&filE=sEarch&Eid=1&quEry=Jargon FilE">Jargon FilE] (1995-04-25)

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