quineprogrammas

Quineprogrammas, or quines, are computer programs that print their own source code when executed, without reading external input. They demonstrate self-reference in a concrete, executable form and are studied in programming language theory and puzzle culture.

The term quine was popularized by Douglas Hofstadter in Gödel, Escher, Bach and named in honor of the logician Willard Van Orman Quine. The idea rests on fixed points in computation: a program that, when run, yields a representation of itself.

Most direct quines exploit a two-part structure: a fragment that outputs a textual representation of another fragment and a second fragment that provides that text, arranged so that the concatenation reproduces the full program. In practical terms, a quine uses string literals and the program’s own control flow to reconstruct its source.

Quines can be direct, requiring no input and printing exactly their source, or indirect, consisting of two separate programs that print each other. There are also multilingual quines that print source in multiple languages and quine relays that pass the self-printing through several languages.

The construction of quines is related to Kleene’s recursion theorem, which guarantees the existence of fixed points for computable transformations. Quines are primarily exercises in self-reference and language syntax rather than practical tools.

A widespread use is educational or recreational: programmers study quines to learn about language features, parsing, and string handling; they also appear in programming contests and code-golf communities.