Welcome to HCODX Online Compiler
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Compile and run Retina code online instantly with HCODX. Our free cloud-based Retina compiler supports real-time execution, standard input, syntax highlighting, and code download. No installation or configuration required. Start coding in Retina now.
Run Retina instantly without installing any IDEs or configuring environments. Our cloud-based Retina handles libraries, runtimes, and dependencies automatically so you can focus on writing code.
Whether you are studying algorithms in Retina, practicing data structures in Retina, or exploring functional programming, our tool provides real-time stdout/stderr feedback with interactive standard input support.
HCODX is a free online compiler and code runner: write code in your browser, execute it on a cloud sandbox, and interact with your program through a live terminal. Students use it for coursework and interview practice; developers use it to test snippets in 85+ languages without setting up a local environment.
Regex is the entire language in Retina, created in 2015 by Martin Ender, a prolific Code Golf Stack Exchange contributor and moderator, on top of the .NET regex engine. A Retina program is a sequence of stages, most simply pairs of lines where the first is a pattern and the second a replacement, applied repeatedly to a working string that starts as the input. Counting matches, sorting, transliteration, and looping stage groups round out the model, proving that string rewriting alone is a complete computational paradigm. Retina answers with their trademark multi-line simplicity remain beloved on Code Golf Stack Exchange. HCODX runs it in an authentic terminal session, so piping your own input into a stage pipeline happens interactively with no .NET setup.
K`Hello, World!
How it works: the K before the backtick marks this stage as a constant, replacing the working string with the text after the backtick regardless of input. When the program ends, Retina prints the working string, so the greeting is the entire output.Retina is the definitive tool for challenges that are fundamentally string rewriting: transliteration, balancing brackets, unary arithmetic, and pattern-counting problems often golf shorter here than in any general-purpose language. It is equally valuable as regex pedagogy, since building whole programs from patterns forces mastery of lookarounds, balancing groups, and .NET-specific features, and esolang fans appreciate it as the cleanest proof that iterated find-and-replace is Turing complete. HCODX is a free online Retina editor, runner and interpreter — an IDE-grade compiler and playground to write and run code online, execute code with live output and live preview, no downloads or web server required.
Single regex matching is not, but Retina iterates: a loop stage reapplies its pattern-replacement until the working string stops changing, and stages can be grouped and nested. Iterated string rewriting is equivalent to a semi-Thue system, a classically Turing-complete model, so Retina can simulate arbitrary computation, and community members have written programs like binary arithmetic and Brainfuck interpreters to demonstrate it.
Because regexes see digits as characters, not quantities. Representing a number as a run of identical characters turns arithmetic into length manipulation: addition is concatenation, and matching with backreferences implements division and primality tests, including the famous prime-checking regex. Retina provides conversion stages between decimal and unary so answers can meet normal I/O formats while computing in unary internally.
The .NET flavor, which is part of its power: it offers variable-length lookbehind and balancing groups, features most engines lack, and both are heavily exploited in golfed answers. Retina 1.0 also layers its own conveniences on top, including stage configuration via backtick options, character-class shorthands, and extensions that make common golfing patterns shorter than raw .NET syntax.
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