Logo the Logo programming language

The Logo programming language is an imperative programming language. It is an adaptation by Wally Feurzeig and Seymour Papert of the Lisp programming language that is easier to read; it has been called Lisp without the parentheses. Today, it is known mainly for its "turtle graphics", but it also has significant facilities for handling lists, files, and I/O. Logo can be used to teach most computer science concepts, as UC Berkeley Professor Brian Harvey does in his "Computer Science Logo Style" trilogy. It can also be used to prepare "microworlds" for students to investigate.

Logo was created in 1966 at BBN, a Cambridge research firm, by Wally Feurzeig and Seymour Papert. Its intellectual roots are in artificial intelligence, mathematical logic and developmental psychology. The first four years of Logo research, development and teaching work was done at BBN. The first implementation was written in LISP on a PDP-1. Its name was "ghost". The goal was basic problem solving; the turtle gave immediate (non-written) feedback so bugs could be spotted. Lots of other effects have been proposed as causes. Power was not a significant factor in the design. However, ease of use for non-typists who had to use a Teletype, was a big consideration, plus informative error comments.

The turtle was a rather late innovation. Logo is not too much different now from the basic concepts before the first turtle. The first turtle was a radio controlled (wireless) floor roamer named "Irving". Irving had touch sensors and could do forward, back, right, left (rotations), and ding (Irving had a bell). The earliest school users were at Muzzy Jr High, Lexington MA.

Implementations of Logo

There are over 130 implementations of Logo, each of which has its own strengths. A popular cross-platform implementation is UCBLogo. MSWLogo, its freeware Windows derivative, is commonly used in schools in the United Kingdom. Comenius Logo is available in Dutch, German, Czech etc. SOLI Logo was a French version widely used in primary schools in the 1980s. In 1984, ExperLogo for the Macintosh added turtles in 3D and on the surface of spheres. It was also compiled instead of interpreted and hence was very fast. Lego/Logo was a system for controlling the turtle or Lego motors and sensors, and was often used in the classroom in the mid 90's. ARLOGO is an Arabic Port of UCBLOGO, considered the first open-source programming language in Arabic.

A modern derivative of Logo is a variation that allows thousands of "turtles", each moving independently. There are two popular implementations: MIT StarLogo and NetLogo. These derivatives allow for the exploration of emergent phenomena and come with many experiments in social studies, biology, physics, and many other sciences. Although the focus is on the interactions of a large number of independent agents, these variations still capture the original flavor of Logo.

There is no single agreed-upon Logo language definition or standard, only a loose tradition. As a result, there are substantial differences between the many dialects of Logo that have evolved. The code examples shown below would work in many Logo dialects, but not all.

The idea is that a turtle with a pen strapped to it can be instructed to do simple things like move forward 100 spaces or turn around. From these building blocks you can build more complex shapes like squares, triangles, circles--using these to draw houses or sail boats.

The turtle moves with commands that are relative to its own position, "LEFT 90" meant rotate left by 90 degrees. A student could understand (and predict and reason about) the turtle's motion by imagining what they would do if they were the turtle. Papert called this "body syntonic" reasoning.

The idea of turtle graphics is also useful for example in Lindenmayer system for generating fractals.

The following is an example of Turtle code. While seemingly very simple, turtles can be given groups of instructions, essentially creating libraries of more complex commands. In practice short forms are used. For example, "LEFT 90" is written "LT 90". Key words are usually written in upper case for beginners, but more advanced texts use lower case.

FORWARD 100
LEFT 90
FORWARD 100
LEFT 90
FORWARD 100
LEFT 90
FORWARD 100
LEFT 90

The language

Logo is an interpreted language. It is not case dependent, but retains the case used for formatting. It is written in lines. It is a compromise between a sequential programming language with block structures, and a functional programming language. There is no 'standard' LOGO, but UCBLogo is highly regarded. It is a teaching language but its list handling facilities make it remarkably useful for producing useful scripts.

This article discusses the major developments in the history of programming languages.

The first programming languages predate the modern computer. From the first, the languages were codes. Herman Hollerith realized that he could encode information on punch cards when he observed that railroad train conductors would encode the appearance of the ticket holders on the train tickets using the position of punched holes on the tickets. Hollerith then proceeded to encode the 1890 census data on punch cards which he made the same size as the boxes for holding US currency. (The dollar bill was later downsized.)

Like many "firsts" in history, the first modern programming language is hard to identify. From the start, the restrictions of the hardware defined the language. Punch cards allowed 80 columns, but some of the columns had to be used for a sorting number on each card. Fortran included some keywords which were the same as English words, such as "IF", "GOTO" (go to) and "CONTINUE". The use of a magnetic drum for memory meant that computer programs also had to be interleaved with the rotations of the drum. Thus the programs were more hardware dependent than today.

To some people the answer depends on how much power and human-readability is required before the status of "programming language" is granted. Jacquard looms and Charles Babbage's Difference Engine both had simple, extremely limited languages for describing the actions that these machines should perform. One can even regard the punch holes on a player piano scroll as a limited domain-specific programming language, albeit not designed for human consumption.

The 1940s

In the 1940s the first recognizably modern, electrically powered computers were created. The limited speed and memory capacity forced programmers to write hand tuned assembly language programs. It was soon discovered that programming in assembly language required a great deal of intellectual effort and was error-prone.

In 1945, Konrad Zuse published details of his programming language Plankalkül. However, it was not implemented in his time and his original contributions were isolated from other developments because Germany was isolated during the war.

Some important languages that were developed in this time period include:

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  1943 - Plankalkül (Konrad Zuse)
  
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  1943 - ENIAC coding system
  
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  1949 - C-10
  

In the 1950s the first three modern programming languages whose descendants are still in widespread use today were designed:

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  FORTRAN, the "FORmula TRANslator", invented by John W. Backus et al.;
  
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  LISP, the "LISt Processor", invented by John McCarthy et al.;
  
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  COBOL, the COmmon Business Oriented Language, created by the Short Range Committee, heavily influenced by Grace Hopper.
  

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  The use of Backus-Naur Form (BNF) for describing the language's syntax. Nearly all subsequent programming languages have used a variant of BNF to describe the context-free portion of their syntax.
  
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  The introduction of lexical scoping for names in arbitrarily nested scopes.
  

Some important languages that were developed in this time period include:

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  1951 - Regional Assembly Language
  
• 
  1952 - Autocode
  
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  1954 - FORTRAN
  
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  1958 - LISP
  
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  1958 - ALGOL
  
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  1959 - COBOL
  
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  1962 - APL
  
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  1962 - Simula
  
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  1964 - BASIC
  
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  1964 - PL/I
  

The period from the late 1960s to the late 1970s brought a major flowering of programming languages. Most of the major language paradigms now in use were invented in this period:

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  Simula, invented in the late 1960s by Nygaard and Dahl as a superset of Algol 60, was the first language designed to support object-oriented programming. Smalltalk (mid 1970s) provided a complete ground-up design of an object-oriented language.
  
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  C, an early systems programming language, was developed by Dennis Ritchie and Ken Thompson at Bell Labs between 1969 and 1973.
  
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  Prolog, designed in 1972 by Colmerauer, Roussel, and Kowalski, was the first logic programming language.
  
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  ML built a polymorphic type system (invented by Robin Milner in 1978) on top of Lisp, pioneering statically typed functional programming languages.
  

The 1960s and 1970s also saw considerable debate over the merits of "structured programming", which essentially meant programming without the use of GOTO. This debate was closely related to language design: some languages did not include GOTO, which forced structured programming on the programmer. Although the debate raged hotly at the time, nearly all programmers now agree that, even in languages that provide GOTO, it is bad style to use it except in rare circumstances. As a result, later generations of language designers have found the structured programming debate tedious and even bewildering.

Some important languages that were developed in this time period include:

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  1970 - Pascal
  
• 
  1972 - C
  
• 
  1972 - Smalltalk
  
• 
  1972 - Prolog
  
• 
  1973 - ML
  
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  1978 - SQL
  

The 1980s were years of relative consolidation. C++ combined object-oriented and systems programming. The United States government standardized Ada, a systems programming language intended for use by defense contractors. In Japan and elsewhere, vast sums were spent investigating so-called "fifth generation" languages that incorporated logic programming constructs. The functional languages community moved to standardize ML and Lisp. Rather than inventing new paradigms, all of these movements elaborated upon the ideas invented in the previous decade.

However, one important new trend in language design was an increased focus on programming for large-scale systems through the use of modules, or large-scale organizational units of code. Modula, Ada, and ML all developed notable module systems in the 1980s. Module systems were often wedded to generic programming constructs---generics being, in essence, parameterized modules (see also parametric polymorphism).

Although major new paradigms for programming languages did not appear, many researchers expanded on the ideas of prior languages and adapted them to new contexts. For example, the languages of the Argus and Emerald systems adapted object-oriented programming to distributed systems.

The 1980s also brought advances in programming language implementation. The RISC movement in computer architecture postulated that hardware should be designed for compilers rather than for human assembly programmers. Aided by processor speed improvements that enabled increasingly aggressive compilation techniques, the RISC movement sparked greater interest in compilation technology for high-level languages.

Language technology continued along these lines well into the 1990s. However, the adoption of languages has always been driven by the adoption of new computer systems, and in the mid-1990s one of the most important new systems in computer history suddenly exploded in popularity.

Some important languages that were developed in this time period include:

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  1983 - Ada
  
• 
  1983 - C++
  
• 
  1985 - Eiffel
  
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  1987 - Perl
  
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  1989 - FL (Backus)
  

The rapid growth of the Internet in the mid-1990s was the next major historic event in programming languages. By opening up a radically new platform for computer systems, the Internet created an opportunity for new languages to be adopted. In particular, the Java programming language rose to popularity because of its early integration with the Netscape Navigator web browser, and various scripting languages achieved widespread use in developing customized applications for web servers. Neither of these developments represented much fundamental novelty in language design; for example, the design of Java was a more conservative version of ideas explored many years earlier in the Smalltalk community, but the widespread adoption of languages that supported features like garbage collection and strong static typing was a major change in programming practice.

Some important languages that were developed in this time period include:

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  1990 - Haskell
  
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  1990 - Python
  
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  1991 - Java
  
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  1993 - Ruby
  
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  1994 - PHP
  
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  2000 - C#
  

Programming language evolution continues, in both industry and research. Some current directions:

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  Mechanisms for adding security and reliability verification to the language: extended static checking, information flow control, static thread safety.
  
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  Alternative mechanisms for modularity: mixins, delegates, aspects.
  
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  Component-oriented software development.
  
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  Increased emphasis on distribution and mobility.
  
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  Integration with databases, including XML and relational databases.
  
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  Open Source as a developmental philosophy for languages, including recent languages such as Python, Ruby, and Squeak.
  
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  Support for Unicode so that source code (program text) is not restricted to those characters contained in the ASCII character set; allowing, for example, use of non-Latin-based scripts or extended punctuation.
  

Fortran (Formula translation)

Algol (Algorithmic Languages)Lisp (Lisp)

Cobol (Common Business-Oriented Language)

APL (A Programming Language or Array Processing Language)

Snobol (String-Oriented Symbolic Language)

PL/1
1967

BCPL (Basic Combined Programming Language)
1968

LOGO
1969

Smalltalk

B

Forth

Prolog (Programming en Logique)

Pascal

Icon
1971

sh
1974

ANSI Cobol 74

Clu (Cluster)

MS Basic 2

ANSI PL/1

ANSI Fortran 77

Ada

Rexx (Restructured extended executor)

Smalltalk-80

C with classes
1982

PostScript

C++
1984

Common Lisp

SML (Standard Meta-Language)

ANSI Cobol 85

Eiffel
1987

Perl (Practical Extraction and Report Language)
1989

ANSI C
1991

Fortran 90

Java

VB (Visual Basic)

CMM (C minus minus)

JavaScript

Jscript

Object Oriented Cobol

Object Rexx(Restructured extended executor)
2000

Java 2

VB.NET