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Вы можете ознакомиться и скачать презентацию на тему Programming paradigms. Доклад-сообщение содержит 28 слайдов. Презентации для любого класса можно скачать бесплатно. Если материал и наш сайт презентаций Mypresentation Вам понравились – поделитесь им с друзьями с помощью социальных кнопок и добавьте в закладки в своем браузере.

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Programming Paradigms

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Programming Paradigm A way of conceptualizing what it means to perform computation and how tasks to be carried out on the computer should be structured and organized. Imperative : Machine-model based Functional : Equations; Expression Evaluation Logical : First-order Logic Deduction Object-Oriented : Programming with Data Types

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Imperative vs Non-Imperative Functional/Logic programs specify WHAT is to be computed abstractly, leaving the details of data organization and instruction sequencing to the interpreter. In constrast, Imperative programs describe the details of HOW the results are to be obtained, in terms of the underlying machine model.

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Illustrative Example Expression (to be computed) : a + b + c Recipe for Computation: Intermediate Code T := a + b; T := T + c; Accumulator Machine Load a; Add b; Add c Stack Machine Push a; Push b; Add; Push c; Add

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Imperative vs Non-Imperative Functional/Logic style clearly separates WHAT aspects of a program (programmers’ responsibility) from the HOW aspects (implementation decisions). An Imperative program contains both the specification and the implementation details, inseparably inter-twined.

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Procedural vs Functional Program: a sequence of instructions for a von Neumann m/c. Computation by instruction execution. Iteration. Modifiable or updateable variables.

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Functional Style : Illustration Definition : Equations sum(0) = 0 sum(n) = n + sum(n-1) Computation : Substituition and Replacement sum(2) = 2 + sum (2-1) = … = 3

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Paradigm vs Language Imperative Style i := 0; sum := 0; while (i < n) do i := i + 1; sum := sum + i end; Storage efficient

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Role of Variables Imperative (read/write) i 0 1 2 3 ... sum 0 1 3 6 ... Functional (read only) i1 sum1 i2 sum2 i3 sum3 ...

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Bridging the Gap Tail recursive programs can be auomatically optimized for space by translating them into equivalent while-loops. func sum(i : int, r : int) : int; if i = 0 then r else sum(i-1, n+r) end Scheme does not have loops.

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Analogy: Styles vs Formalisms Iteration Tail-Recursion General Recursion

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Logic Programming Paradigm Integrates Data and Control Structures edge(a,b). edge(a,c). edge(c,a). path(X,X). path(X,Y) :- edge(X,Y). path(X,Y) :- edge(X,Z), path(Z,Y).

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Declarative Programming A logic program defines a set of relations. This “knowledge” can be used in various ways by the interpreter to solve different queries. In contrast, the programs in other languages make explicit HOW the “declarative knowledge” is used to solve the query.

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Append in Prolog append([], L, L). append([ H | T ], L, [ H | R ]) :- append(T, L, R). True statements about append relation. “.” and “:-” are logical connectives that stand for “and” and “if” respectively. Uses pattern matching. “[]” and “|” stand for empty list and cons operation.

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Different Kinds of Queries Verification sig: list x list x list append([1], [2,3], [1,2,3]). Concatenation sig: list x list -> list append([1], [2,3], R).

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More Queries Constraint solving sig: list x list -> list append( R, [2,3], [1,2,3]). sig: list -> list x list append(A, B, [1,2,3]). Generation sig: -> list x list x list append(X, Y, Z).

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Object-Oriented Style Programming with Abstract Data Types ADTs specify/describe behaviors. Basic Program Unit: Class Implementation of an ADT. Abstraction enforced by encapsulation. Basic Run-time Unit: Object Instance of a class. Has an associated state.

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Procedural vs Object-Oriented Emphasis on procedural abstraction. Top-down design; Step-wise refinement. Suited for programming in the small.

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Integrating Heterogeneous Data In C, Pascal, etc., use Union Type / Switch Statement Variant Record Type / Case Statement In C++, Java, Eiffel, etc., use Abstract Classes / Virtual Functions Interfaces and Classes / Dynamic Binding

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Comparison : Figures example Data Square side Circle radius Operation (area) Square side * side Circle PI * radius * radius

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Adding a new operation Data ... Operation (area) Operation (perimeter) Square 4 * side Circle 2 * PI * radius

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Adding a new data representation Data ... rectangle length width Operation (area) ... rectangle length * width

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Procedural vs Object-Oriented New operations cause additive changes in procedural style, but require modifications to all existing “class modules” in object-oriented style. New data representations cause additive changes in object-oriented style, but require modifications to all “procedure modules”.

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Object-Oriented Concepts Data Abstraction (specifies behavior) Encapsulation (controls visibility of names) Polymorphism (accommodates various implementations) Inheritance (facilitates code reuse) Modularity (relates to unit of compilation)

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Example : Role of interface in decoupling Client Determine the number of elements in a collection. Suppliers Collections : Vector, String, List, Set, Array, etc Procedual Style A client is responsible for invoking appropriate supplier function for determining the size. OOP Style Suppliers are responsible for conforming to the standard interface required for exporting the size functionality to a client.

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Client in Scheme (define (size C) (cond ( (vector? C) (vector-length C) ) ( (pair? C) (length C) ) ( (string? C) (string-length C) ) ( else “size not supported”) ) )) (size (vector 1 2 (+ 1 2))) (size ‘(one “two” 3))

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Suppliers and Client in Java interface Collection { int size(); } class myVector extends Vector implements Collection { } class myString extends String implements Collection { public int size() { return length();} } class myArray implements Collection { int[] array; public int size() {return array.length;} } Collection c = new myVector(); c.size();

Теги Programming paradigms

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