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Development of Low-Level Languages
All computers operate by following machine language programs, a long sequence of instructions called machine code that is addressed to the hardware of the computer and is written in binary notation (see numeration), which uses only the digits 1 and 0. First-generation languages, called machine languages, required the writing of long strings of binary numbers to represent such operations as “add,” “subtract,” “and compare.” Later improvements allowed octal, decimal, or hexadecimal representation of the binary strings.
Because writing programs in machine language is impractical (it is tedious and error prone), symbolic, or assembly, languages—second-generation languages—were introduced in the early 1950s. They use simple mnemonics such as A for “add” or M for “multiply,” which are translated into machine language by a computer program called an assembler. The assembler then turns that program into a machine language program. An extension of such a language is the macro instruction, a mnemonic (such as “READ”) for which the assembler substitutes a series of simpler mnemonics. The resulting machine language programs, however, are specific to one type of computer and will usually not run on a computer with a different type of central processing unit (CPU).
Evolution of High-Level Languages
The lack of portability between different computers led to the development of high-level languages—so called because they permitted a programmer to ignore many low-level details of the computer's hardware. Further, it was recognized that the closer the syntax, rules, and mnemonics of the programming language could be to “natural language” the less likely it became that the programmer would inadvertently introduce errors (called “bugs”) into the program. Hence, in the mid-1950s a third generation of languages came into use. These algorithmic, or procedural, languages are designed for solving a particular type of problem. Unlike machine or symbolic languages, they vary little between computers. They must be translated into machine code by a program called a compiler or interpreter.
Early computers were used almost exclusively by scientists, and the first high-level language, Fortran [Formula translation], was developed (1953–57) for scientific and engineering applications by John Backus at the IBM Corp. A program that handled recursive algorithms better, LISP [LISt Processing], was developed by John McCarthy at the Massachusetts Institute of Technology in the early 1950s; implemented in 1959, it has become the standard language for the artificial intelligence community. COBOL [COmmon Business Oriented Language], the first language intended for commercial applications, is still widely used; it was developed by a committee of computer manufacturers and users under the leadership of Grace Hopper, a U.S. Navy programmer, in 1959. ALGOL [ALGOrithmic Language], developed in Europe about 1958, is used primarily in mathematics and science, as is APL [A Programming Language], published in the United States in 1962 by Kenneth Iverson. PL/1 [Programming Language 1], developed in the late 1960s by the IBM Corp., and ADA [for Ada Lovelace], developed in 1981 by the U.S. Dept. of Defense, are designed for both business and scientific use.
BASIC [Beginner's All-purpose Symbolic Instruction Code] was developed by two Dartmouth College professors, John Kemeny and Thomas Kurtz, as a teaching tool for undergraduates (1966); it subsequently became the primary language of the personal computer revolution. In 1971, Swiss professor Nicholas Wirth developed a more structured language for teaching that he named Pascal (for French mathematician Blaise Pascal, who built the first successful mechanical calculator). Modula 2, a Pascallike language for commercial and mathematical applications, was introduced by Wirth in 1982. Ten years before that, to implement the UNIX operating system, Dennis Ritchie of Bell Laboratories produced a language that he called C; along with its extensions, called C++, developed by Bjarne Stroustrup of Bell Laboratories, it has perhaps become the most widely used general-purpose language among professional programmers because of its ability to deal with the rigors of object-oriented programming. Java is an object-oriented language similar to C++ but simplified to eliminate features that are prone to programming errors. Java was developed specifically as a network-oriented language, for writing programs that can be safely downloaded through the Internet and immediately run without fear of computer viruses. Using small Java programs called applets, World Wide Web pages can be developed that include a full range of multimedia functions.
Fourth-generation languages are nonprocedural—they specify what is to be accomplished without describing how. The first one, FORTH, developed in 1970 by American astronomer Charles Moore, is used in scientific and industrial control applications. Most fourth-generation languages are written for specific purposes. Fifth-generation languages, which are still in their 06/98infancy, are an outgrowth of artificial intelligence research. PROLOG [PROgramming LOGic], developed by French computer scientist Alain Colmerauer and logician Philippe Roussel in the early 1970s, is useful for programming logical processes and making deductions automatically.
Many other languages have been designed to meet specialized needs. GPSS [General Purpose System Simulator] is used for modeling physical and environmental events, and SNOBOL [String-Oriented Symbolic Language] is designed for pattern matching and list processing. LOGO, a version of LISP, was developed in the 1960s to help children learn about computers. PILOT [Programmed Instruction Learning, Or Testing] is used in writing instructional software, and Occam is a nonsequential language that optimizes the execution of a program's instructions in parallel-processing systems.
There are also procedural languages that operate solely within a larger program to customize it to a user's particular needs. These include the programming languages of several database and statistical programs, the scripting languages of communications programs, and the macro languages of word-processing programs.
Compilers and Interpreters
See R. Cezzar, A Guide to Programming Languages: Overview and Comparison (1995), T. W. Pratt and M. V. Zelkowitz, Programming Languages: Design and Implementation (3d ed. 1996); C. Ghezzi and M. Jazayem, Programming Language Concepts (3d ed. 1997); R. W. Sebasta, Concepts of Programming Languages (4th ed. 1998).
BASIC has become the leading cause of brain-damage in proto-hackers. This is another case (like Pascal) of the cascading lossage that happens when a language deliberately designed as an educational toy gets taken too seriously. A novice can write short BASIC programs (on the order of 10-20 lines) very easily; writing anything longer is painful and encourages bad habits that will make it harder to use more powerful languages. This wouldn't be so bad if historical accidents hadn't made BASIC so common on low-end micros. As it is, it ruins thousands of potential wizards a year.
Originally, all references to code, both GOTO and GOSUB (subroutine call) referred to the destination by its line number. This allowed for very simple editing in the days before text editors were considered essential. Just typing the line number deleted the line and to edit a line you just typed the new line with the same number. Programs were typically numbered in steps of ten to allow for insertions. Later versions, such as BASIC V, allow GOTO-less structured programming with named procedures and functions, IF-THEN-ELSE-ENDIF constructs and WHILE loops etc.
Early BASICs had no graphic operations except with graphic characters. In the 1970s BASIC interpreters became standard features in mainframes and minicomputers. Some versions included matrix operations as language primitives.
A public domain interpreter for a mixture of DEC's MU-Basic and Microsoft Basic is here. A yacc parser and interpreter were in the comp.sources.unix archives volume 2.
See also ANSI Minimal BASIC, bournebasic, bwBASIC, ubasic, Visual Basic.
BASIC(Beginners All purpose Symbolic Instruction Code) A programming language developed by John Kemeny and Thomas Kurtz in the mid-1960s at Dartmouth College. Originally developed as an interactive timesharing language for mainframes, BASIC was widely used on the first personal computers. Microsoft's BASIC helped make the Altair the first commercial success of an assemble-it-yourself microcomputer (see Altair). See timesharing, Business Basic and Visual Basic.
Compiler and Interpreter
BASIC is available in both compiler and interpreter form. As an interpreter, the language is conversational and can be debugged a line at a time. It can also be used as a quick calculator.
BASIC is considered one of the easiest programming languages to learn, and simple programs can be quickly written on the fly. The following BASIC example converts Fahrenheit to Celsius:
10 INPUT "Enter Fahrenheit "; FAHR 20 PRINT "Celsius is ", (FAHR-32) * 5 / 9