The history of computer programming is rich with self-reflexive language games, games which either code self-reflexivity into algorithmic machine instructions or algorithmic instructions into everyday language. Perhaps the most basic example of the former are "Quines", program sourcecode which, as a software equivalent of von Neumann's self-reproducing automata, generates an exact copy of itself (see <http://www.nyx.net/~gthompso/quine.htm>) while recursive acronyms like "GNU" for "GNU's Not Unix" (which iterates infinitely when dissected into its component words) may be the the most promiment example of the latter.
From the opposite angle, there is a longer history of artists and poets using computer instruction and protocol code as material. In its 1962 manifesto, the French Oulipo group around the poet Raymond Queneau and the mathematician Francois le Lionnais proposed to use computers for poetic games, process text with Markov chains (just as a number of more contemporary digital arts works like Charles O. Hartman's and Hugh Kenner's "Virtual Muse" poems, Ray Kurzweil's "Cybernetic Poetic" and Cornelia Sollfrank's "Net.art generators") and write poetry in the Algol programming language. In the early 1970s, Le Lionnais and Noël Arnaud published poetry written in Algol code which, just as the early Perl Poetry of Larry Wall and Sharon Hopkins from 1990. Even where their code did not properly compile and run on computers, it took artistic advantage of the fact that any digital code is potentially machine-executable and at least twice readable as sourcecode and output. In comparison to digital artforms whose output is not code, Algol and Perl poems even have the potential to contaminate and short-circuit both instances of digital data.
While no other form of net art and net poetry is structurally as closely linked to computing as programming code poetry, more recent net art and net poetry takes an aesthetic step beyond the former in modelling its language after programming and protocol code without strictly reproducing its logic. The code poetry of, among others, mez, Alan Sondheim and Ted Warnell seems to build on two developments a) the re-coding of traditional pictorial ASCII art into amimetical noise signals by net artists like Jodi, antiorp, mi-ga and Frederic Madre, (b) the mass-proliferation of programming language syntax through web and multimedia scripting languages and search engines. For the reader of mez's "netwurks", it remains all the more an open question whether the "mezangelle" para-code of parentheses and wildcard characters only mimicks programming languages or is, at least partially, the product of programmed text filtering.
In my view, code poetry reveals that digital poetry has been misperceived in the last ten years, with too much attention for elborate interfaces - "hypertext" itself is nothing more than such an interface - and too little attention for structures coded into its very language.