A program in Karel is used to control a simple robot named Karel that lives in an environment consisting of a grid of streets and avenues. Karel understands five basic instructions: move, turnLeft, putBeeper, pickBeeper, and turnoff. Karel can also perform booleanqueries about his immediate environment, asking whether there is a beeper where he is standing, whether there are barriers next to him, and about the direction he is facing. A programmer can create additional instructions by defining them in terms of the five basic instructions, and by using conditional control flow statements if and while with environment queries, and by using the iterate construct.
Variants and descendants
The language has inspired the development of various clones and similar educational languages. As the language is intended for beginners, localized variants exist in some languages, notably Czech. The principles of Karel were updated to the object-oriented programmingparadigm in a new programming language called Karel++. Karel++ is conceptually based on Karel, but uses a completely new syntax, similar to Java. A REALbasic implementation, rbKarel, provides the basic Karel commands within an RBScript environment with BASIC syntax being used for loops and conditionals. This teaching project provides a cross-platform GUI for Karel experiments including single-stepping and spoken output. A Karel-inspired language and environment called Robot Emil uses a 3D view of the robot's world. Robot Emil offers a large palette of objects that can be placed to depict walls, windows, water and grass. The camera may be moved freely throughout the 3D environment. The robot may be controlled interactively with buttons in the GUI, or by programs written in Emil's Karel-like programming language. The author states that the program is free for use by schools, students and children. Versions are available in English, Czech and Slovak. A proprietary language which is also called Karel is used to program the robots of FANUC Robotics. However, FANUC Karel is derived from Pascal. The language has also been implemented as Karel the Dog in JavaScript by CodeHS. Similar to the original language, this implementation features Karel in a grid world. Programmers use and build upon Karel's simple vocabulary of commands to accomplish programming tasks. Instead of putting and picking beepers, Karel the Dog puts and takes tennis balls.
