| Karel the Robot | |
|---|---|
 | |
| Paradigm | procedural |
| Designed by | Richard E. Pattis |
| First appeared | 1981 |
| Website | xkarel |
| Dialects | |
| Some localized language variants | |
| Influenced by | |
| Pascal | |
| Influenced | |
| Karel++,AgentSheets,Guido van Robot | |
Karel is aneducational programming language for beginners, created byRichard E. Pattis in his bookKarel The Robot: A Gentle Introduction to the Art of Programming. Pattis used the language in his courses atStanford University,California. The language is named afterKarel Čapek, aCzech writer who introduced the wordrobot in his playR.U.R.[1][2]
Aprogram in Karel is used to control a simplerobot named Karel that lives in an environment consisting of a grid of streets (left-right) and avenues (up-down). Karel understands five basic instructions:move (Karel moves by one square in the direction he is facing),turnLeft (Karel turns 90 ° left),putBeeper (Karel puts a beeper on the square he is standing at),pickBeeper (Karel lifts a beeper off the square he is standing at), andturnoff (Karel switches himself off, the program ends). Karel can also performboolean queries 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. Aprogrammer can create additionalinstructions by defining them in terms of the five basic instructions, and by using conditionalcontrol flow statementsif andwhile with environment queries, and by using theiterate construct.[citation needed]
The following is a simple example of Karel syntax:
BEGINNING-OF-PROGRAM DEFINE turnRight AS BEGIN turnLeft; turnLeft; turnLeft; END BEGINNING-OF-EXECUTION ITERATE 3 TIMES BEGIN turnRight; move END turnoff END-OF-EXECUTION END-OF-PROGRAM
The following implementation is Karel in thePython programming language.[3] Other implementations are available.
The following are the primitive functions.
move()turn_left()put_beeper()pick_beeper()paint_corner(COLOR_NAME)Karel programs are structured in the following way:
# is a comment and is ignored by the interpreter.def, followed by the function name and parentheses. The body of the function follows in subsequent lines.main(): A program run executes themain function. The other functions are not executed unless called.Karel can respond to certain conditions in its world:
front_is_clear(),beepers_present(),beepers_in_bag(),left_is_clear(),right_is_clear(),facing_north(),facing_south(),facing_east(), andfacing_west()And their inverses:
front_is_blocked(),no_beepers_present(),no_beepers_in_bag()left_is_blocked(),right_is_blocked(),not_facing_north(),not_facing_south(),not_facing_east(), andnot_facing_west().It can also check the current block's color bycorner_color_is(COLOR_NAME).
There are two control structures:
if andelse.for andwhile.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, notablyCzech (the programming language was quite popular inCzechoslovakia).
The principles of Karel were updated to theobject-oriented programming paradigm in a new programming language called Karel++. Karel++ is conceptually based on Karel, but uses a completely new syntax, similar toJava.
A REALbasic implementation, rbKarel,[4] 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 calledRobot Emil[5] uses a3D view of the robot's world.Robot Emil offers a large palette of objects that can be placed to depict walls, windows (transparency), 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 inEnglish,Czech andSlovak.
A proprietary language which is also called Karel is used to program the robots ofFANUC Robotics. However, FANUC Karel is derived fromPascal.
The language has also been implemented as Karel the Dog inJavaScript byCodeHS. 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.
A German version of Karel is named "Robot Karol".[6]
