Introduction

Question 1

Classifying Languages 1

Answer 1

Languages are commonly classified by their core paradigm. But this isn’t an exact science!

• Imperative / Procedural
  
  • Controlled flow of operations that effect a programs state.
  • e.g., C, assembler [*]sh, Postscript, OpenGL, Logo, Scratch, Javascript, Python
• Object Oriented
  
  • Imperative with implicit encapsulation of data and functions
  • e.g., C++, Java, C#, Javascript, Python
• (Pure) Functional
  
  • Declarative languages with no explicit state
  • Haskell, Erlang, (Python?)
• Declarative
  
  • Describes logic of program with minimal explicit control of the flow of execution.
  • SQL, HTML, Regex

Question 2

Classifying Languages 2

Answer 2

▪ Languages are also classified by technical design choices…

▪ Statically typed
▪ The type of a variable is explicitly defined and fixed at the time that variable is created
▪ Return types of functions/methods are also explicitly defined

▪ Dynamically typed
▪ Variables are typically not explicitly defined at all
▪ Type of a variable is inferred from its use, and can change in the lifetime of a program

▪ Compiled
▪ Programs are translated into a low level language (e.g. machine code) before they are run
▪ The high level language is then typically not directly involved at run time

▪ Interpreted
▪ The program is read (by another program) and each ‘token’ (e.g. a line of code) executed one at a time
▪ Based on the result of that execution, program flow may move to a different place in the file

Question 3

Classifying Languages 3

Answer 3

▪ …as they directly impact the external characteristics

▪ Platform Independence
▪ Allowing a program to run on a range of platforms without adaptation

▪ Safety
▪ Verifying that a program operates as intended
▪ Scoping, type safety and immutability

▪ Expressivity
▪ How closely individual instructions relate to a users intent
▪ Closely related to the notion of code density – how much code is needed to represent a program.

▪ Performance / Efficiency
▪ How much resource is needed to execute a given program (e.g. CPU / RAM)
▪ How efficiently the language translates to hardware and its optimisations (e.g. instruction/data parallelism)
▪ Which brings other considerations to bear…