Logo (programming language)
Loops may be nested, giving spectacular results with little effort. The analogy of a turtle with a pen attached to its tail is often used. It was interfaced with Lego bricks, although Lego decided later to use another language in the commercial Lego Mindstorms products.An interface also exists for Cricket robots. ObjectLOGO is a variant with object-oriented extensions. Logo3D is a tridimensional version of LOGO and can be found at . TurtleTracks, an opensource Logo implementation in Java, was designed and implemented by Daniel Azuma, based on BSD Logo (with various extensions). It was designed and implemented by George Birbilis. LOGO was a primary influence on the Smalltalk programming language.
Papert called this body-syntonic reasoning. The earliest year-long school users of Logo were in 1968-69 at Muzzey Jr High, Lexington MA.
sum takes two parameters and is an operation , thus the calculation is possible. The process is the same, except that in the former a line is deposited on the display device and in the latter a line is removed.
Boxer was developed at MIT and Berkeley. . In the editor, procedures may be written over many lines, as nothing is interpreted until the edit is complete. The new word is saved into the available vocabulary, but the definition will be lost once the Logo session is over.
They allow for the exploration of emergent phenomena and come with many experiments in social studies, biology, physics, and other areas. Most Logos are 2D, but the Elica interpreter is notable for supporting 3D graphics. It is a compromise between a sequential programming language with block structures, and a functional programming language.
It is an adaptation and dialect of the Lisp language; some have called it Lisp without the parentheses. Internally procedures are words and in this case, any time CHAIR is entered, the sequence REPEAT 4 would repeat the CHAIR operation four times. Mathematics in Logo uses prefix notation, like: sum :x :y, product :x :y, difference :x :y, quotient :x :y.
Most of those 197 are no longer in wide use, but many are still under active development. As yet there is no single agreed-upon Logo language definition or standard, though there is a broad consensus on core aspects of the language. Turtle geometry works somewhat differently from (x,y) addressed Cartesian geometry, rather operating in a Euclidean space (i.e., relative measures and angles without an origin, unlike coordinate-addressed systems such as PostScript).
There are two popular implementations: MIT s StarLogo and CCL s NetLogo. It can be used to teach most computer science concepts, as UC Berkeley Lecturer Brian Harvey does in his Computer Science Logo Style trilogy. Logo was created in 1967 at Bolt, Beranek and Newman (BBN), a Cambridge, Massachusetts research firm, by Wally Feurzeig and Seymour Papert and informative error messages.
The turtle moves with commands that are relative to its own position, LEFT 90 meant rotate left by 90 degrees. An approximation of a circle can be constructed easily with 360 small rotations and a step forward: REPEAT 360 .
It passes the information by value and the colon is pronounced as the value of. Logo is not case-sensitive but retains the case used for formatting.
Apple Logo, which was developed by LCSI, was the most broadly used and prevalent early implementation of Logo. The closest thing to a de facto Logo standard today is UCBLogo, also known as Berkeley Logo. For instance, the idea of turtle graphics is also useful in Lindenmayer system for generating fractals. Logo is generally known as an interpreted language, although recently there have been developed compiled Logo dialects—such as Lhogho or Liogo.
The use of virtual Turtles allowed for immediate visual feedback and debugging. The first working turtle robot was created at MIT in 1969. The virtual and physical turtles were first used by fifth graders at the Bridge School in Lexington, MA in 1970-71. Logo s best-known feature is the turtle, which is an on-screen cursor (derived originally from a robot of the same name), which can be given movement and drawing instructions, and is used to programmatically produce line graphics.
There are substantial differences between the many dialects of Logo. The turtle s pen can be lifted and lowered, thus drawing a rudimentary dotted line. Logo was designed in spirit of low threshold and no ceiling, which enables easy entry by novices and yet meet the needs of high-powered users.
Although most often used for graphics, Logo can also control robots. There are several of these template commands with names like MAP, APPLY, FILTER, FOREACH, REDUCE and CASCADE.
The situation is confused by the regular appearance of turtle graphics programs that mistakenly call themselves Logo. Logo use peaked in the early-to-mid 1980s, largely due to marketing of Apple Logo (for the Apple II computer) and TI LOGO (for the TI 99/4A) to primary school educators, emphasizing Logo s usefulness in teaching computing fundamentals to novice programmers. It was later ported to .NET / J# by George Birbilis. E-Slate Logo is an enhancement of TurtleTracks Logo with Object-oriented programming (OOP) primitives (TELL, ASK, EACH and TELLALL).
It is a teaching language but its list handling facilities make it remarkably useful for producing useful scripts. There are three datatypes in UCBLogo, A number is a special case of word. There is no static typing. Arrays are also provided. Logo provides several common control structures. There are iteration commands Recursion is Logo s preferred processing paradigm. Logo also provides list-based control structures.
x := y + 3) is handled in Logo with the make command: or make takes 2 parameters, the second of which here is sum :y 3. Calling a procedure with inputs (the name usually used for arguments in the Logo literature) also creates local variables that hold the argument values. Logo inherits lists from Lisp, and they are its primary method of storing vectors.
This makes the input less onerous. From a programmatical perspective, the first argument to make is passed by reference, while the second is passed by value. Variables don t have to be declared before use; their scope is then global. A variable may be declared local, then its scope is limited to that procedure and any procedures that it calls (a.k.a.
In Unix tradition the input stream can be changed, so input can come from a disk file. Using the turtle analogy, the turtle s pen must paint, and the turtle s pen must erase. In UCBLogo, the turtle can be set to erase using the command PENERASE (PE).
MSWLogo and its successor FMSLogo, for Microsoft Windows, are commonly used in schools in the United Kingdom and Australia. Today, it is known mainly for its turtle graphics, but it also has significant facilities for handling lists, files, I/O, and recursion. Logo was created in 1967 for educational use, more so for constructivist teaching, by Daniel G.
UCBLogo has only a rudimentary graphical user interface, so several projects exist that provide a better interface. MSWLogo also supports a windows interface thus I/O is available through this GUI- and keyboard and mouse events can trigger interrupts. Simple GIF animations may also be produced on MSWlogo version 6.5 with the gifsave command. Some modern derivatives of Logo allow thousands of independently moving turtles.
The colon is used for this purpose. Anything written after the ; (semicolon) is ignored, allowing the coder to insert comments. The Hello World program in Logo looks like this: There are three loop (repeat) commands; REPEAT is one.
Turtle graphics were added to the Logo language by Seymour Papert in the late 1960s to support Papert s version of the turtle robot, a simple robot controlled from the user s workstation that is designed to carry out the drawing functions assigned to it using a small retractable pen set into or attached to the robot s body. As a practical matter, the use of turtle geometry instead of a more traditional model mimics the actual movement logic of the turtle robot. The procedure, (word) is instructed to expect something and give that something a name.
3 evaluates to 3, and :y takes the contents of the thing called y, these are summed giving a number. The effect of make is to place the result into the first parameter. Now any future FD movements will erase anything beneath them.
Most Logo implementations are interpreted, but some compilers have been built, including the Lhogho compiler, by the same author as Elica. It is also the main influence on the Etoys educational programming environment and language, which is essentially a Logo written in Squeak (a variant of Smalltalk). LOGO provided the underlying language for Boxer.
The basic idea is of two lists: each of the commands is applied in turn to each of the data items. 2 is really 2 Variable assignment (eg.
Modern Logo has not changed too much from the basic concepts before the first turtle. Similarly, output can be redirected. Commands may be written on one line, or more.
It is free and cross-platform. Infix is also available. Logo allows for recursion, the process where a procedure calls itself. As of March 2009 there were 197 implementations and dialects of Logo, each with its own strengths.
Many commands have mnemonic short forms; for example FORWARD and RIGHT are coded FD and RT respectively. Later, BBN developed a turtle named Irving that had touch sensors and could move forwards, backwards, rotate, and ding its bell.
LOGO (an acronym for Logic Oriented Graphic Oriented) is a computer programming language used for functional programming. Animations require both the ability to draw shapes and to erase shapes.
The pen can be restored with the command PENPAINT (PPT). A WAIT delay between the drawing and the erasing introduces the illusion of motion. Logo can pass extra information to its words, and return information. dynamic scope).
Examples include emptyp, wordp, and listp. Procedures can be defined on the command line, using the TO END pair: However, in some early Logos the procedure is limited to the physical line length of the input device. All Logos can invoke an Editor, usually by EDALL. The interpreter detects the datatype by context. There are two important symbols This is an extremely useful symbol that keeps reminding students that a variable is really some place in memory. A number is a special case of self evaluation—it really could be written with a quote.
(See also: command-query separation, where a query is an operation in Logo). Bobrow, Wally Feurzeig and Seymour Papert.
The first turtle was a tethered floor roamer, not radio-controlled or wireless. MSWLogo allows input from COM ports and LPT ports and also hardware ports.
There are three commands to process property list. Text may be written to the command window (output stream) using print and to the graphics window using label The standard commands are readlist readword readchar with the normal input stream being the keyboard. A special subset of operations, called predicates, which just output the word true or false, are conventionally written with a final p.
A student could understand (and predict and reason about) the turtle s motion by imagining what they would do if they were the turtle. There is no standard LOGO, but UCBLogo is highly regarded.
It is traditionally and most often represented pictorially either as a triangle or a turtle icon (though it can be represented by any icon). A display turtle preceded the physical floor turtle.
Some Logo implementations, particularly those that allow the use of concurrency and multiple turtles, support collision detection and allow the user to redefine the appearance of the turtle cursor, essentially allowing the Logo turtles to function as sprites. Turtle geometry is also sometimes used in environments other than Logo as an alternative to a strictly coordinate-addressed graphics system. They represent four flavours of template iteration, known as explicit-slot, named-procedure, named-slot (or Lambda), and procedure-text. A property list is a special list where the odd number items are property names, and the even are property values.
This draws a square. The command FD 100 LEFT 90 is executed four times. Commercial Logos that are still widely used in schools include MicroWorlds Logo and Imagine Logo. MSWLogo supports multiple turtles, and 3D Graphics.
When the procedure is run with a command such as CHAIR 200, the word :thesize takes the value 200 so when FD :thesize is executed, the interpreter understands FD, the value of 200. Each line is made up of function calls, or subroutines in programming terminology, of which there are two types: A command is similar to a Pascal procedure, and an operation is similar to a Pascal function.
