Programming Languages definitions

programming language

programming language

A formal language which comprises a set of instructions that produce various kinds of output. Consists of instruction for computers

Program

instructions for a computer to execute

high-level language

Language that allows you to write precise instructions in a human-readable form

Program Design

Design of a language driven to fix a problem

Program Philosophy/Paradigm

• Imperative (Procedual)

• Declarative (Functional)

• Logical/Constrained-based (OOP)

Computer Architecture

Language must be made to work how the hardware architecture works

Language Implementation Technology:

Compilers, Interpreters, Virtual Machines

Compiler:

Translates source code into executable machine code run directly by the hardware

Interpreter:

Reads and executes each line of code as it reads it during run time.

Virtual Machine

Executes a compiled intermediate level code, byte code, which is interpreted by the virtual machine

Desirable design features of a language:

• Simplicity

• Orthogonality

• Level of Abstraction

• Portability

• Cost *Expressiveness

simplicity

Feature set is short and to the point

Orthogonality:

Different factors combine to produce something meaningful

level of abstraction:

The amount of complexity by which a system is viewed or programmed. Higher level, less detail. Lower level, more detail.

Portability

Ability to move program from one system to another

Expressivity

The amount of ways that the same problem can be solved.

Memory Allocation

• Static Allocation

• Dynamic Allocation

Static Allocation:

Memory is allocated at compilation time (predetermined) PROS: *Faster CONS: *Needs to know amount of memory in advance *Prone to memory waste

Dynamic Allocation:

memory space is only allocated when required at runtime. PROS: *Do not need to know amount of memory in advance *Use only what is needed CONS: *Slower

Memory Allocation Implementation:

• Compiler: Static and Dynamic

• Interpreter: Dynamic

• Virtual Machine: Static and Dynamic

Names:

User generated ID's (function names, class names, variable names)

case sensitive:

Distinguishing upper- and lowercase characters. Easier to implement.

case-insensitive:

Both the uppercase and lowercase forms of a character are considered by a computer program to be the same

reserved words

Words that have predefined meanings that cannot be changed. *Keywords: private, void, static, etc. 25. Identifiers: names given to entities, such as variables, functions, structures, etc.

Variable:

Location in memory that is subject to destructive update which is bound to a name. Value can change overtime.

L-Value:

address location of variable in memory

R-value:

Actual value that is stored in the memory address location

Aliasing

One part of memory has multiple names leading to it

Symbol Table

A data structure that links names to information about the objects denoted by the names. Keeps track of binding between name and memory locations.

Storage

*Statically Allocated Variables *Dynamically Allocated Variables

Binding

the association of a name with a variable or value. Also, the time when it happens

Types of binding

*Static binding *Dynamic binding

Static Binding:

Binding performs before program runs

Dynamic Binding:

Binding performs while program is running

Static Typing:

Types are checked before program runs PROS: *Faster Execution time *Readability in increased CONS: *No flexibility *More initial overhead

Dynamic Typing:

Types are checked while program is running PROS: *Flexibility (no need to explicitly write type annotation) *Less initial overhead before deployment CONS: *Slower Execution Time *Decreased Readability

Type annotation:

*Explicit *Implicit

Explicit Typing:

Language demands the programmer explicitly state type

Implicit Typing:

Language does no demand explicit denotation of data

Destructive Updates

Any change to a memory location that replaces the current value

Scope

Region in program in which the lifetime of a name is defined. Lexical region in which a name is visible/usable *Nested functions *Blocks *Order of declaration *Global variables

Static Scope

Region is defined using lexical features, delimiters. *A region in a text of the program *Implemented using "blocks"

Dynamic Scope

: Value is determined by the identifier associated with the most recent environment

Scope Blocks:

Lexical region in program where a name is visible

Constants:

Value can not be changed

Data Types:

Primitive Data Types *Integral numbers *Floating point numbers *Boolean types *Character

Integral Numbers:

Int: 32 bits = 4 bytes Byte: 8 bits = 1 byte Short: 16 bits = 2 bytes Long: 64 bits= 8 bytes

floating point numbers:

Float: 32 bits = 4 bytes Double: 64 bits = 8 bytes

Boolean type

Boolean: 8 bits = 1 byte bool: 8 bits = 1 byte

Character:

character: 8 bits = 1 byte char: 8 bits = 1 byte

string type:

-a string is a sequence of characters -the String type is used to declare variables that store strings -is not a primitive type: it is known as a class or reference type -one or more characters in double quotes -strings as character arrays

Types of strings:

-Dynamic size up to a bound (array) -Constant size (immutable)

Pointer

Special variables that allow access to l-values of memory locations

Syntax

the rules for combining words into grammatically sensible sentences in a given language

Semantics:

the set of rules by which we derive meaning from morphemes, words, and sentences in a given language; also, the study of meaning

lexicon:

Valid words of the language. A dictionary; a specialized vocabulary used in a particular field or place

grammar:

a set of rules that specify how the units of language can be combined to produce meaningful messages and sentences.