Introduction

1. Different Generation of Languages

• No agreement among the authors about the proper demarkation
• Machine language, Assembly language (symbols instead of numerci code), Third generation (FORTRAN, C, Pascal), 4GL (Application specific such as Powerhouse), Fifth generation languages (Prolog)
• Machine language - every detail is specified
• Prolog - Very few details are specified

1. Why high level languages?

• pages 7-8
  • readibility
  • portability
  • library support
  • limited syntax checking
• UNIX was written in C
• Section 1.2 describes some of the problems associated with writing correct programs
• Any debugging effort is essentially limited by the human imagination
• If you organize your programs properly, it is easier to spot the errors

1. Paradigms
   • Imperative
   • Functional
   • Object oriented
   • Logical

• Generally, if you know one language from a paradigm, it is possible to learn another language from the same paradigm fairly easily.

1. Imperative

• FORTRAN system (was not proposed as a language). Demonstrated that translated code can be bettern than most machine language programmers.
• Fortran did not provide facilities for structured programming
• Algol 60 was an effort to rectify many of the shortcomings
  • Pascal: Developed for education use
  • C: Developed as an implementation language
• Functional programming
  • Lisp (List Processing)
  • Was and still is a popular language for AI programming
  • Symbolic manipulations
  • ISWIM (tried to remove Lot of Inconvenient Stupid Parantheses)
  • Fig. 1.4 shows other descendants of Lisp
  • Just as the imperative programmers have C++, Function programming also have object orinted flavor in languages such as CLOS

1. Object oriented languages

• Simula
  • Used for simulation
  • C++ comes from the imperative side
  • Smalltalk more of a system than a language

1. Logic Programming

• Prolog
  • Uses limited subset of logic called Horn Clause logic
  • Specify the logical rules
  • Ask questions - the system will use the logic to answer the question

1. Translators

• Compiler
  • Translates a high level program and creates a machine laguage copy of the program
  • Essentially bringing the program down to the machine level
  • Faster than machine code written by average machine language programmer but slower than the machine code written by good machine language programmer
  • Faster than interpreted programs
• Interpreter
  • Does not translate the entire program in its entirety into the machine language
  • Translation is done one instruction at a time
  • Every time the program is run the translation has to take place
  • Interpreter can be looked at as a virtual machine that understands and executes higher level instruction
  • Advantages: dynamic programs, can do some run time tricks that are not easily possible in compiled programs