Programming Languages Master Set - Test #1

What is a programming language?

Programmers use programming languages to instruct computers to do things.

Syntax

The structure of programs (tokens

Semantics

The expected behavior of a given syntactical construct.

Meaning of a language

• Describes the effects of executing the code

• Difficult to provide a comprehensive description of meaning in al contexts

Programming language

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

What did John von Neumann propose?

proposed that computers should be permanently hardwired with a small et of general-purpose operations.

Opcode

the first 4 bits of a line of code

indicates the type of operation to be performed

Next 12 bits contain code for the instructions operands.

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

FORTRAN

FORmula TRANslation language

• developed by John Backus in the early 1950s

• Reflected the architecture of a particular type of machine

• lacked the structured control statements and data structures of later high-level language

ALGOL

ALGOrighmic Language released in 1960.

• Provided a standard notation for computer scientists to publish algorithms in journals.

• Included structured control statements for sequencing (begin-end blocks)

Compiler

Translates programming language statements into machine code

ALGOL was the first language to receive a formal specification or definition

Pascal

language for teaching programming in the 1970s

Descended form ALGOL

Ada

For embedded applications of U.S Dept of Defense

Lambda Calculus

Computational model developed by mathematician Alonzo Church

Based on the theory of recursive functions.

Lisp

Programming language that uses the functional model of computation

What are the two types of programming abstractions?

Data abstraction Control Abstraction

Data Abstractions

Simplify the behavior and attributes of data for humans

Ex: numbers, character strings, search trees, standard mathematical operations

simplify the behavior and attributes of data for humans

Control Abstractions

simplify properties of the transfer of control

Examples: loops

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

Basic data abstraction

Hides internal representation of common data values.

Values are also called "primitive' or "atomic" because the programmer cannot normally access the component parts or bits of the internal representation

Variables

Use of symbolic names to hide computer memory locations containing data values

Data types

names given to kinds of data values

Declaration

The process of giving a variable a name and a data type

Data Structure

collects related data values into a single unit

Hides component parts but can be constructed from parts

Array

a sequence of individually indexed items with the same data type

Information Hiding

defining new data types (data and operations) that hide information

Unit abstraction

often associated with the concept of an abstract data type

a set of data values and the operations on those values

Interface

a set of operations available to the user

Implementation

Internal representation of data values and operations

Unit abstraction also provides ___________________

Reusability

Typically __________ are entered into a __________ and become the basis for library mechanisms

components, library

Application programming interface (API)

gives information about the resource's components

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

Ex: x += 10 instead of x = x+10

Branch Instructions

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

Iterator

an object associated with a collection (such as array

Procedure (or subprogram or subroutine)

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

Procedure Declaration

names a procedure and associates it with the actions to be performed

invocation (or procedure activation)

the act of calling the procedure

Parameters

values that can change from call to call

Arguments (or actual parameters)

values supplied by the caller for the parameters

Runtime environment

The system implementation of the program

• Stores information about the condition of the program and the way procedures operate

Function

closely related to a procedure

• returns a value or result to its caller

• can be written to a correspond more closely to mathematical abstractions

Recursion

a mechanism that further exploits the abstraction mechanism.

Higher-order Functions

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

map functions

expects another function and a collection as arguments

applies the argument functions to each element in the argument collection and returns a list of results

Unit

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

Allows a program to be understood as a whole without needing to know the details of the services provided by the unit

Threads

other programs executing outside the Java system

Task

mechanism in Ada for parallel execution

Imperative Language

a language with three properties -Sequential execution of instructions -Use of variables representing memory locations -Use of assignment to change the values of variables

Paradigm

Pattern

von Neumann Bottleneck

requirement that a program be described as a sequence of instructions

Functional Paradigm

Based on the abstract notion of a function in lambda calculus

Logic Paradigm

Based on symbolic logic

Object-oriented paradigm

Reusable code that operates in a way to mimic behaviors of real-world objects

Language Syntax

similar to the grammar of a natural language

Grammar

formal definition of the language's syntax

Lexical structure

structure of the language's words

similar to spelling in natural languages

Tokens

the language's words

includes keywords

Are there any generally accepted formal methods for describing semantics

No.

Translator

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

What are the two major types of translators

Interpreter and Compiler

Interpreter

Executes a program directly

Compiler

Produces an equivalent program in a form suitable for execution

Compilation requires at least two steps...

Source program - input to the compiler

Target program - output from the compiler

What must a target program be?

• Translated by an assembler into an object program

• Linked with other object programs

• Loaded into appropriate memory locations

Target language may be ____ _____

byte code

Byte code

a form of low-level code

Virtual machine

written differently for different hardware architectures

Efficiency of execution

primary design criterion

• Early FORTRAN code more or less directly mapped to machine code

Writability

the quality of a language that enables a programmer to use it to express computation clearly

Efficiency

usually thought of as efficiency of the target code

Programmer efficiency

how quickly and easily can a person read and write in the programming language?

Expressiveness

how easy is it to express complex processes and structures?

Regularity

refers to how well the features of a language are integrated

Languages that satisfy the criterion of regularity are said to adhere to the _________________

principle of least astonishment

Regularity can be subdivided into three concepts

• Generality

• Orthogonal design

• Uniformity

Generality

achieved by avoiding special cases in the availability or use of constructs and by combining closely related constructs into a single more general one

Orthogonal design

constructs can be combined in any meaningful way

Uniformity

a design in which similar things look similar and have similar meanings while different things look different

Can classify a feature or construct as irregular if it lacks one of these three qualities

Value Semantics

Values are copied during assignment

Reference semantics

Two references to the same object

Security

is the program going to make the computer crash?

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

Macro

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

Availability

a lot of people coding it

Portability

easy to move between cpus