short notes: Functional Programming

Functional Programming: -

Languages- Pascal, C, Modula 2, Ada, are imperative languages Because basic construct is a command
Heavily Influenced by Von Neumann architecture - includes a store (memory), on instruction used to identify the next instruction to be fetched from store
computation model has control structures did Determine the sequencing of instructions- use assignments to make incremental modifications to the store.

Properties (Imperative Languages): -

Principal operation- assignment of values to variables
programs are command oriented-> They carry out algorithms with statement level sequence control, selection and repetition Usually by
Programs are organized as Blocks-> DataControl is dominated by scope rules
computing is done by effect (changes to the store)

Computing: -

Intrinsic to imperative programming plays havoc with some of the mathematical properties- essential to prove the correctness of programs.
Example: - Is addition commutative Inn on imperative program, Doesburg write (a + b) always produce the same value as write (b + a).

Most likely give different results for the two versions of this program. DEPENDING on the order of evaluation of expressions

Anomaly is Caused by the side effects in the expression being Evaluated
Programming by effect lies at the heart of imperative programming.
If we depend on imperative programs we must discard many of the basic properties of mathematics (associative, commutative, law of addition and multiplication and the distributive law for multiplication over addition.

Functional Programming: -

Provides paradigm of alternative notion of programming
Avoids the problem of side effects
Functional languages Concerned with the Data Objects and value instead of variable

Values: -

Functions: -

* Functional language supplies primitive functions

* Programmer uses function constructors to define new functions

* Program Execution is by evaluation of expression

* Sequence Control depends on selection and recursion

Pure Functional language: -

No assignments language
Values are Communicated by the use of parameters to functions.
thesis restrictions enforce a discipline on the programmer did Avoids Side Effects
Functional languages - referentially transparent

Principle of Referential Transparency: -

value of the function is Determined by the values of its arguments and the context in Which the function application Appears.
It is independents of the History of the execution
Evaluation of a function with the same argument Produces the same result every time it is invoked
An expression will produce the same value each time it is Evaluated in a Given Context
Guarantees the validity of the property substituting equals for equals.

LISP: -

List Processing [1956]
started with on Artificial Intelligence Group at MIT under John McCarthy
Implemented (1960) on an IBM 704 (McCarthy and his students).
Had the first Fortran implementation
Early Example of interactive computing
original development used expression S (S- symbolic language)
Lisp with 2M expression (intention of developing Algol like version)
When Lisp interpreter written in Lisp what with S Lisp expression Which Dropped 2
Principle version based on Lisp 1.5 include Interlisp, FranzLisp, MacLisp, CommonLisp and Scheme
High level notation for selection
Fuctions are defined as expressions
Repetitive tasks by recursions
Parameters are passed to functions by value
Program Consists -> set of function definitions Followed by a list of expression did may include function evaluation.

Scheme syntax: -

Scheme version chosen Because of small size and uniform treatment of functions
BasicObject in Scheme - S expression

short notes