Programming Paradigms

Three Major Paradigms

• Imperative (sometimes called procedural)
• Object-Oriented
• Functional
• There are others:
  • Logic, Declarative
  • Visual Languages
  • Event-driven
  • Scripting and special-purpose languages, e.g.,String Processing Languages
  • Parallel and concurrent languages

Brief History of Programming Languages (and Paradigms)

• Machine Language → Assembly → Macros & Pseudo-Instructions

  e.g., MOVE $t2, $t1 → ADD $t2, $t1, $zero

• Fortran: How big a jump is this?

  Accumulator-based Assembly	FORTRAN (c. 1957)
  Put data1 into Accumulator Add data2 to Accumulator Move contents of Accumulator	CSQRD = A**2 * B**2 HUGE!

• What Fortran has in common with Assembler:
  

  Imperative — based on von Neumann architecture: state-driven fetch-execute-store virtual machine

• Slow evolution to higher levels of abstraction:

  	Procedural			Object-Oriented
  Algol (c. 1960)	→	Pascal (1970) / C (1972)	→	C++ (c. 1983)
  	⮑	Simula (c. 1969)	→	Smalltalk (c. 1980)

• Key features of Object-Oriented Programming (OOP):

  objects / data abstraction, classes as first-class types, message passing / dynamic binding, inheritance

  dynamic binding ⟶ can be hard to predict or follow the flow of control

  ➡ To really understand the difference between imperative and object-oriented, we need to look at Structure Design vs. Object-Oriented Design (OOD).
• Event-driven: A programming paradigm, even if not a class of languages

  • Set up things that can respond to events
  • Write the responses
  • Control-flow is driven by events (user events, system events, etc.)

• BUT There was also a huge jump in abstraction in 1959!

  Functional: LISP

  • Language based on mathematical functions and λ-calculus
  • Key Ideas:
    • Functions as 1^st-class entities
    • No state
    • atoms & lists; functions and data have same form (lists)