CS374: History of Programming Languages

Bill Mongan

Evolution of Language

Machine Language

• Look up the opcode and manipulate registers directly (add, subtract, etc.)

Ada Lovelace Programs Babbage’s Analytical Engine

• 1840: Babbage’s Analytical Engine design

Zuse Plankalkul

• Conceptual High-Level Language in the 1940’s
• Local boolean variables (just 1 bit!)
  • User-defined types and arrays allowed
• Pass-by-value
• Conditionals and iteration

Imperative Languages

• One step at a time
• Manipulate a variable
• Procedures are compositions of these imperative instructions

LET x = x + 1
LET y = x * 2

Fortran

• 1957: Formula Translator

Fortran

• 3-Way IF statements (0, negative, positive)
• DO Loops
• Subroutines
• Semantics: Variables beginning with the letters I through N assumed to be integers

COBOL

• 1959: Common Business Oriented Language
• DoD CODSYL committee effort based on Grace Hopper’s FLOW-MATIC design
• Data records (similar to a linked list)
• Code block demarcation i.e. END-IF
• GO TO staetments

BASIC

• 1964: Programming for non-STEM
• Events: Visual Basic
• ON ERROR GOTO...

C

• 1972: Dennis Ritchie
• long and unsigned data types
• static variable scope
• Weak, unenforced types define data “shape” but not contents
• Pointers

Python

• 1991: Interpreted Language
• Extensive Library System
• Return of indented code blocks
• Dynamic typing and Garbage Collection

Declarative Languages

• Statements describe the outcome, not the implementation
• Concise, easy to write, but complex instructions can be more difficult to read

arr = np.array([0, 1, 2, 3, 4, 5])
evens = np.where(arr % 2 > 0, arr*2, arr)

Declartaive Paradigms: Logic Programming

• 1972: Prolog

prereq(cs173, cs174).
prereq(cs174, cs374).
?- prereq(cs173, cs174).
Yes

Declarative Paradigms: Functional Programming

• 1970’s: Scheme - Descendent of List Processor (LISP, 1958)
• Composition of local functions that operate on tuples with minimal side effects

(define square
  (lambda(n)
    (* n n)))
      
(square 5)

Object-Oriented Languages

• Generally imperative with declarative infusion
• Oriented around manipulating data structures
• Encapsulation, Polymorphism, Inheritance

Smalltalk

• 1972: Dynamic (declared) types
• Disambiguating assignment operator = to :=
• Messages: 2 squared

Ada

• 1980’s to Present
• Descendant of ALGOL
• Record types

C++

• 1985: Descendant of C
• Combine the low-level nearness to the machine of C with high level object abstractions
• References as an abstraction of pointers
• Significant standard template library

Java

• 1995: Descendant of C
• Everything is a class
• Encapsulation
• Strong type enforcement
• Exception handling

Today

• A blend of popular ideas
  • Go: Channels and routines for concurrency
  • Rust, Ruby, Objective-C
  • Pythonic declarative statements