# Modular Descriptions of Regular Functions

## TL;DR

This paper explores different formal methods for describing string-to-string transformations, comparing automata-based operational approaches with more human-readable descriptions using basic transformations and combinators.

## Contribution

It introduces a unified perspective on formal descriptions of string transformations, highlighting the advantages of human-friendly formalisms alongside automata-based models.

## Key findings

- Automata-based descriptions enable direct implementation with deterministic input scanners.
- Human-friendly descriptions simplify understanding and designing string transformations.
- Combinators extend basic transformations to express complex string operations.

## Abstract

We discuss various formalisms to describe string-to-string transformations. Many are based on automata and can be seen as operational descriptions, allowing direct implementations when the input scanner is deterministic. Alternatively, one may use more human friendly descriptions based on some simple basic transformations (e.g., copy, duplicate, erase, reverse) and various combinators such as function composition or extensions of regular operations.