Programming languages are the medium of expression in the art of computer programming. An ideal programming language will make it easy for programmers to write programs succinctly and clearly. Because programs are meant to be understood, modified, and maintained over their lifetime, a good programming language will help other read programs and understand how they work. Software design and construction are complex tasks. Many software systems consist of interacting parts. These parts, or software components, may interact in complicated ways. To manage complexity, the interface and communication between components must be designed carefully. A good language for large-scale programming will help programmers manage the interaction among software components effectively. In evaluating programming languages, we must consider the tasks of designing, implementing, testing, and maintaining software, asking how well each language supports each part of the software life cycle.

PROGRAMMING LANGUAGES HISTORY

Hundreds of programming languages have been designed and implemented over the last 50 years. As many as 50 of these programming languages contained new concepts, useful refinements, or innovations worthy of mention. Because there are far too many programming languages to survey, however. We concentrate on six programming: LispMLCC++Smalltalk, and Java. Together, these languages contain most of important language feature that have been invented since higher-level programming languages emerged from the primordial swamp of assembly language programming around 1960.

     The history of modern programming languages begins 1958_1960 with the development of Algol, Cobol, Fortran, and Lisp.

      In the 1950s, a number of languages were developed to simplify the process of writing sequences of computer instructions. In this decade, computers were very primitive by modern standards. Most programming was done with the native machine language of the underlying hardware. This was acceptable because programs were small and efficiency was extremely important. The two most important programming language developments of the 1950s were Fortan and Cobol.

      Fortran was developed at IBM around 1954_1956 by a team led by John Backus. The main innovation of Fortran (a contraction of formula translator) was that it became possible to use ordinary mathematical notation in expressions. For example, the Fortran expression for adding the value of I to twice the value of j is i + 2*j. Before the development of Fortran, it might have been necessary to place i in a register, place j in a register, multiply j times 2 and then add the result to i. Fortran allowed programmers to think more naturally about numerical calculation by using symbolic names for variables and leaving some details of evaluation order to the compiler. Fortran also had subroutines (a form of procedure of function), arrays, formatted input and output, and declarations that gave programmers explicit control over the placement of variables and arrays in memory. However, that was about it. To give you some idea of the limitations of Fortran, many early Fortran compilers stored numbers 1, 2, 3, … in memory locations, and programmers could change the values of numbers if they were not careful! In addition, it was not possible for a Fortran subroutine to call itself, as this required memory management techniques that had not been invented yet.

     Cobol is programming language designed for business applications. Like Fortran programs, many Cobol programs are still in use today, although current versions of Fortran and Cobol differ substantially forms of these languages of the 1950s. The primary designer of Cobol was intended to resemble that of common English. It has been suggested in jest that if object-oriented Cobol were a standard today, we would use “add 1 to Cobol giving Cobol” instead of “C++”.

       Lisp and Algol, come out around 1960. These languages have stack memory management and recursive functions or procedures. Lisp provides higher-order functions (still not available in many current languages) and garbage collection, whereas the Algol family of languages provides better type systems and data structuring. The main innovations of the 1970s were methods for organizing data, such as records (or structs), abstract data types, and early forms of objects. Objects became mainstream in the 1980s, and 1990s brought interest in network-centric computing, interoperability, and security and correctness issues associated with active content on the internet. The 21st century promises greater diversity of computing devices, cheaper and more powerful hardware, and increasing interest in correctness, security, and interoperability.

CONCEPTS AND LANGUAGES

There are many important language concepts and many programming languages.