CSC302 2006S, Class 3: A Biased History of Programming Languages

Admin:
* Sorry about Wednesday - You get one additional free sick day
* Sorry about the confusion about "Homework 1"
* Please submit comments on readings by midnight the night prior to class
* Readings on the design of languages:
  * N. Wirth - Designed Pascal
  * C.A.R. Hoare - Designed Quicksort

Overview
* Dating key ideas and issues
* An approximate history

/What Errors Did You Find?/
* Why does Sam ask?
  * To embarass Davis
  * To remind you never to take readings as absolute truth
  * To remind you to read carefully, particularly code
* The DEFUN should not be in a comment, p. 53
  (DEFUN equal_lists (lis1 lis2)
     ...
  )
* Problem in C code, p. 81
  * Average won't be precise b/c it's an integer (design?)
  * The array has size 98.  The number of inputs can be of
    size 99.  Whoops! 
  * Why should you have picked up on that (almost immediately)?
    * Good programmers use defined constants instead of hard-coded numbers
    * Typical programming error: Off by one (in comparisons, array defn's, etc.)
  * What is the likely effect?
    * Null pointer error (possible)
    * Possibly overwrite some other piece of data
      * With incorrect output
      * With no observable incorrect output
  * How could a language designer help?
    * Check bounds, probably at run time, report error if bound error
    * Language design to make bounds errors difficult - Original
      design of Pascal
        Arrays take subranges as parameters
        Indices must be members of same subrange type
    * Automatically expand arrays as necessary
      * Can slow down the program
      * Inadvertent expansion is likely an error
  * Language design philosophy conflict
    * Some designers (e.g. Wall): Programmers know what they want to do, don't hamper them
    * Some designers (e.g., Sun Java team): Programmers make endless mistakes.  Stop them!

/Dating Some Key Concepts/
* Computational devices - Thousands of years, eg., abacus
* The general-purpose computer (as opposed to ...) - Instead
  of a different complex machine for each algorithm, build one
  machine that can run different algorithms
  * Designed? 1800's - Babbage
    Programmer - Ada
  * Implemented?  ENIAC, ABC - early 1940's
* Stored program computers - Great idea that programs can be data
  (no patch cords!  Yay) - John von Neumann
* Punch cards
  Late 1700's Jacquard loom
  IBM's predecessor, late 1800's
* The programming language
* The first implemented programming language
* Hypertext

/Dating the Primary Paradigms/
* Imperative programming - Fortran, late 1950's
* Functional programming - LISP, late 1950's early 1960's
* Object-oriented programming - Simula67, mid 1960's
* Logic programming - Prolog, early 1970's
* Parallel programming - 1950's
* Relational model - Mid 1960's

* Declarative is a general term for "program with declarative statements, not with control"
  + Pure Functional
  + Logic
  + Relational
/History of Languages, Approximated/