Programming Language Survey

Programming language

A notation for communicating to a computer what we want it to do.

“Hardwired” Programs

Pre-1940s computers required you to adjust the internal wiring to perform different tasks.

Assembly language

A set of mnemonic symbols for instruction codes and memory locations.

Assembler

A program that translates the symbolic assembly language code to binary machine code.

Loader

A program that loads the machine code into computer memory.

Mnemonic symbols shortcomings

• Lacks abstraction of conventional mathematical notation

• Each type of computer hardware architecture has its own machine language instruction set and requires its own dialect of assembly language

FORTRAN (FORmula TRANslation Language)

• Developed by Backus in early 1950s

• Reflected the architecture of a particular type of machine

• Lacked the structured control statements and data structures of later high-level languages

• Supported algebraic notation and floating point numbers

ALGOL (ALGOrithmic Language)

• Released in 1960

• First language that was machine independent

• First language to receive a formal specification or definition

• Supported different numeric types and control statements

• Introduced arrays

• Supported procedures and recursive procedures

Compiler

Translates programming language statements into machine code.

Pascal

Language for teaching programming in the 1970s.

Ada

Language for embedded applications of U.S. Dept. of Defense.

Lambda Calculus

Computational model developed by mathematician Alonzo Church which is based on the theory of recursive functions

Lisp

Programming language that uses the functional model of computation

Data abstractions

Simplify the behavior and attributes of data for humans

Ex. numbers, character strings, search trees

Control abstractions

Simplify properties of the transfer of control

Ex. loops, conditional statements, procedure calls

Basic abstractions

Collect the most localized machine information

Structured abstractions

Collect intermediate information about the structure of a program

Unit abstractions

• Collect large-scale information in a program

• Often associated with the concept of an abstract data type

• Information hiding: Defining new data types (data and operations) that hide information

• Separates the interface (available operations) from the implementation

• Provides reusability

• Application programming interface (API) gives information about the resource’s components

Basic data abstraction

Hides internal representation of common data values

• Variables: use of symbolic names to hide computer memory locations

• Data types: names given to kinds of data values

• Declaration: process of giving a variable a name and data type

Data structure

• Collects related data values into a single unit

• Constructed from parts which can be hidden, accessed, or modified

Basic control abstractions

Statements that combine a few machine instructions into an abstract statement that is easier to understand.

Syntactic sugar

A mechanism that allows you to replace a complex notation with a simpler, shorthand notation.

Iterator

An object associated with a collection (such as array, list, set, or tree)

Procedure/subprogram/subroutine

• Groups a sequence of actions into a single action that can be called or invoked from other points in the program

• Does not return anything

Function

Mathematical and returns one thing

Method

The message sent to an object to make it do something

Runtime environment

The system implementation of the program

Higher-order functions

Functions that can accept other functions as arguments and return functions as values.

Unit

A stand-alone collection of procedures providing logically related services to other parts of a program.

Ex. Threads, processes, tasks

von Neumann bottleneck

Requirement that a program be described as a sequence of instructions.

Imperative language

Three properties

• Sequential execution of instructions

• Use of variables representing memory locations

• Use of assignment to change the values of variables

Language syntax

Similar to the grammar of a natural language.

Language semantics

• Meaning of a language

• No generally accepted formal method for describing semantics

A language is successful if

• It achieves the goals of its designers

• It attains widespread use in an application area

• It serves as a model for other languages that are successful

Writability

The quality of a language that enables a programmer to use it to express computation clearly, correctly, concisely, and quickly

Regularity

• Refers to how well the features of a language are integrated.

• Should minimize restrictions and strange interactions between constants.

• Principle of least astonishment.

A language designed with security in mind…

• Discourages programming errors

• Allows errors to be discovered and reported

Semantically safe

Languages that prevent a programmer from compiling or executing any statements or expressions that violate the language definition.

Extensible language

A language that allows the user to add features to it.

Ex. New data types or operations

Macro

Specifies the syntax of a piece of code that expands to other standard code when compiled.

Variables in functional programming

• Bound to values not memory locations.

• Its value cannot change, eliminating assignment as an available operation.

Referential transparency

The property whereby a function’s value depends only on the values of its arguments (and nonlocal variables)

Value semantics

Semantics in which names are associated only to values, not memory locations

In functional programming, functions are…

• First-class data values

• They can be computed by other functions and parameters to other functions

LISP (LISt Processing)

First language that contained many of the features of modern functional languages

Tail recursive

When the recursive steps are the last steps in any function

Garbage collection

Automatic memory management technique to return memory used by functions

Higher-order functions

Functions that take other functions as parameters and functions that return functions as values

Static/lexical scope

The area of a program in which a variable declaration is visible

Free variable

A variable referenced within a function that is not also a formal parameter to that function and is not bound within a nested function

Bound variable

A variable within a function that is also a formal parameter to that function

Metalinguistic power

The capacity to build, manipulate, and transform lists of symbols that are then evaluated as programs

Currying

A process in which a function of multiple parameters is viewed as a higher-order function of a single parameter that returns a function of the remaining parameters.

Nonstrict

A property of a function in which delayed evaluation leads to a well-defined result, even though subexpressions or parameters may be undefined.

Lazy evaluation

Only evaluate an expression once it is actually needed

Generator-filter programming

A style of functional programming in which computation is separated into procedures that generate streams and other procedures that take streams as arguments

First-order predicate calculus

A way of formally expressing logical statements

Logic programming

A collection of statements is assumed to be axioms, and from them a desired fact is derived by the application of inference rules in some automated way.

Assembly language

A set of mnemonic symbols for instruction codes and memory locations

Structured control abstractions

Divide a program into groups of instructions nested within tests that govern their execution.

Branch instructions

Instructions that support selection and iteration to memory locations other than the next one.

Recursion

A mechanism that further exploits the abstraction mechanism.

Translator

A program that accepts other programs and either directly executes them or transforms them into a form suitable for execution.

Interpreter

• A type of translator that executes a program directly.

• Operates in one step, directly accepting input and source code.

Compiler

• A type of translator that produces an equivalent program in a form suitable for execution.

• Operates in two steps, taking a source program as input and outputting a target program.

• Target may need to be translated by an assembler into an object program, then linked and loaded.

Efficiency considerations in a language

• Execution

• Target code

• Programmer ability to read and write

• Expressiveness for complex processes

Generality

A concept of regularity which is achieved by avoiding special cases in the availability or use of constructs and by combining closely related constructs into a single more general one.

Ex. In C can’t compare two structures with ==

Orthogonal design

A concept of regularity where constructs can be combined in any meaningful way with no unexpected restrictions or behaviors.

Ex. Pascal only allows scalar or pointer types to be returned.

Uniformity

A concept of regularity which implies a design in which similar things look similar and have similar meanings while different things look different.

Ex. C++ requires extra semicolon after a class definition but not function definition.

Functional programming

• Provides a uniform view of programs as functions

• Treats functions as data

• Provides prevention of side effects

Function

A rule that associates to each x from set X of values a unique y from set Y of values.

Composition

A function takes two functions as parameters and produces another function as its returned value.