In computer humor, a write-only language is a pejorative term for a programming language alleged to have syntax or semantics sufficiently dense and bizarre that any routine of significant size is too difficult to understand by other programmers and cannot be safely edited. Similarly, write-only code is source code so arcane, complex, or ill-structured that it cannot be reliably modified or even comprehended by anyone with the possible exception of the author. Write-only code is also referred to as line noise, suggesting that the code looks like spurious characters from signal noise in the communication line. In such a language it would be more difficult to read, understand, and modify existing source code than to start over and rewrite it from scratch.
A more rarely used term is read-only language, which refers to systems with so many boundary conditions that the code can only be written through constant experimentation and not from first principles. The resulting code is perfectly readable by other programmers, but any attempt to duplicate it in another context will fail.
Languages that are often derided as write-only include APL, Dynamic debugging technique (DDT), Perl, Forth, Text Editor and Corrector (TECO), Mathematica, IGOR Pro and regular expression syntax used in various languages. Attributes that these languages have in common include a large set of operators and a syntax which encourages, or at least permits, the writing of very dense code. Some also have syntaxes which are very different from other languages, and some use different characters sets. The code below for example is Conway's Game of Life as written in APL2:
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- "Conway's Game of Life in one line of APL". Dr.Dobbs. February 2006. Archived from the original on 2015-03-24. Retrieved 2015-03-28.