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Вы можете ознакомиться и скачать презентацию на тему Programming paradigms. Доклад-сообщение содержит 30 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 Procedural Functional Logic Object-Oriented

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Specifying the WHAT Describe the Inputs Specific values Properties Describe the Outputs (as above) Describe the Relationships Between I x O As a possibly infinite table Equations and other predicates between input and output expressions For a given input, output may not be unique

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Specifying the HOW Describe the Inputs Specific values Properties Describe HOW the Outputs are produced Models of existing computers Program State Control Flow A Few Abstractions Block Structure Recursion via a Stack

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Procedural programming Describes the details of HOW the results are to be obtained, in terms of the underlying machine model. Describes computation in terms of Statements that change a program state Explicit control flow Synonyms Imperative programming Operational Fortran, C, … Abstractions of typical machines Control Flow Encapsulation Control Structures Procedures No return values Functions Return one or more values Recursion via stack

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Procedural Programming: State Program State Collection of Variables and their values Contents of variables change Expressions Not expected to change Program State Assignment Statements Other Statements Side Effects

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C, C++, C#, Java Abstractions of typical machines Control Flow Encapsulation Control Structures Procedures No return values Functions Return one or more values Recursion via stack Better Data Type support

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Illustrative Example Expression (to be computed) : a + b + c Recipe for Computation Account for machine limitations Intermediate Location 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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Declarative Programming Specifies WHAT is to be computed abstractly Expresses the logic of a computation without describing its control flow Declarative languages include logic programming, and functional programming. often defined as any style of programming that is not imperative.

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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 updatable variables..

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

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Paradigm vs Language Imperative Style

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Bridging the Gap Imperative is not always faster, or more memory efficient than functional. E.g., tail recursive programs can be automatically translated into equivalent while-loops. func xyz(n : int, r : int) : int; if n = 0 then r else xyz(n-1, n+r) fi endfunc

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Analogy: Styles vs Formalisms Iteration Tail-Recursion General Recursion

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Logic Programming Paradigm 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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Logic 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 ], X, [ H | Y ]) :- append(T, X, Y). True statements about append relation. Uses pattern matching. “[]” and “|” stand for empty list and cons operation.

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

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

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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 Procedural 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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