Retinia

Retinia is a cellular automaton programming language specifically designed for pattern matching and replacement in strings. It operates on a single, global string and performs a sequence of rule applications to transform it. The core of Retinia consists of defining patterns to search for within the string and specifying replacements to be made when those patterns are found.

Retinia programs are typically structured as a series of stages, each containing a set of regular expression-based rules. Each rule consists of a regular expression pattern and a replacement string (which can also be a regular expression). When a stage is executed, Retinia iterates through the rules within that stage. For each rule, it searches the current string for matches to the rule's pattern. If a match is found, the matching portion of the string is replaced with the rule's replacement string. After a replacement is made, the search for further matches restarts from the beginning of the string, allowing for multiple replacements within a single stage.

The language offers various control flow mechanisms to manage the execution of stages, including loops, conditional execution based on the success or failure of rules, and calls to subroutines. These control flow features allow for the creation of complex and sophisticated string manipulation algorithms.

Retinia is often used for tasks involving text processing, code golf, and demonstrating the power of regular expressions. While it is Turing-complete, its design is specifically tailored for string transformations, making it particularly well-suited for problems that can be naturally expressed as a sequence of pattern matching and replacement operations. Its conciseness and expressiveness in this domain have made it a popular tool among programmers interested in string manipulation challenges.